Theory and Simulation Group

Group Leader: Pablo Ordejón

Publications

2017

  • Ab initio study of electron-phonon coupling in rubrene

    Ordejón P., Boskovic D., Panhans M., Ortmann F. Physical Review B; 96 (3, 035202) 2017. 10.1103/PhysRevB.96.035202. IF: 3.836

    The use of ab initio methods for accurate simulations of electronic, phononic, and electron-phonon properties of molecular materials such as organic crystals is a challenge that is often tackled stepwise based on molecular properties calculated in gas phase and perturbatively treated parameters relevant for solid phases. In contrast, in this work we report a full first-principles description of such properties for the prototypical rubrene crystals. More specifically, we determine a Holstein-Peierls-type Hamiltonian for rubrene, including local and nonlocal electron-phonon couplings. Thereby, a recipe for circumventing the issue of numerical inaccuracies with low-frequency phonons is presented. In addition, we study the phenyl group motion with a molecular dynamics approach. © 2017 American Physical Society.


  • Anisotropic features in the electronic structure of the two-dimensional transition metal trichalcogenide TiS3: Electron doping and plasmons

    Silva-Guillén J.A., Canadell E., Ordejón P., Guinea F., Roldán R. 2D Materials; 4 (2, 025085) 2017. 10.1088/2053-1583/aa6b92. IF: 6.937

    Analysis of the band structure of TiS3 single-layers suggests the possibility of changing their physical behaviour by injecting electron carriers. The anisotropy of the valence and conduction bands is explained in terms of their complex orbital composition. The nature of the Fermi surface and Lindhard response function for different doping concentrations is studied by means of firstprinciples DFT calculations. It is suggested that for electron doping levels x (number of electrons per unit cell) ~0.18-0.30e- the system could exhibit incommensurate charge or spin modulations which, however, would keep the metallic state whereas systems doped with smaller x would be 2D metals without any electronic instability. The effect of spin-orbit coupling in the band dispersion is analysed. The DFT effective masses are used to study the plasmon spectrum from an effective low energy model. We find that this material supports highly anisotropic plasmons, with opposite anisotropy for the electron and hole bands.


  • Building Complex Kondo Impurities by Manipulating Entangled Spin Chains

    Choi D.-J., Robles R., Yan S., Burgess J.A.J., Rolf-Pissarczyk S., Gauyacq J.-P., Lorente N., Ternes M., Loth S. Nano Letters; 17 (10): 6203 - 6209. 2017. 10.1021/acs.nanolett.7b02882. IF: 12.712

    The creation of molecule-like structures in which magnetic atoms interact controllably is full of potential for the study of complex or strongly correlated systems. Here, we create spin chains in which a strongly correlated Kondo state emerges from magnetic coupling of transition-metal atoms. We build chains up to ten atoms in length by placing Fe and Mn atoms on a Cu2N surface with a scanning tunneling microscope. The atoms couple antiferromagnetically via superexchange interaction through the nitrogen atom network of the surface. The emergent Kondo resonance is spatially distributed along the chain. Its strength can be controlled by mixing atoms of different transition metal elements and manipulating their spatial distribution. We show that the Kondo screening of the full chain by the electrons of the nonmagnetic substrate depends on the interatomic entanglement of the spins in the chain, demonstrating the prerequisites to build and probe spatially extended strongly correlated nanostructures. © 2017 American Chemical Society.


  • Electrical and Thermal Transport in Coplanar Polycrystalline Graphene-hBN Heterostructures

    Barrios-Vargas J.E., Mortazavi B., Cummings A.W., Martinez-Gordillo R., Pruneda M., Colombo L., Rabczuk T., Roche S. Nano Letters; 17 (3): 1660 - 1664. 2017. 10.1021/acs.nanolett.6b04936. IF: 12.712

    We present a theoretical study of electronic and thermal transport in polycrystalline heterostructures combining graphene (G) and hexagonal boron nitride (hBN) grains of varying size and distribution. By increasing the hBN grain density from a few percent to 100%, the system evolves from a good conductor to an insulator, with the mobility dropping by orders of magnitude and the sheet resistance reaching the MΩ regime. The Seebeck coefficient is suppressed above 40% mixing, while the thermal conductivity of polycrystalline hBN is found to be on the order of 30-120 Wm-1 K-1. These results, agreeing with available experimental data, provide guidelines for tuning G-hBN properties in the context of two-dimensional materials engineering. In particular, while we proved that both electrical and thermal properties are largely affected by morphological features (e.g., by the grain size and composition), we find in all cases that nanometer-sized polycrystalline G-hBN heterostructures are not good thermoelectric materials. © 2017 American Chemical Society.


  • Electrochemical behavior of nanostructured La0.8Sr0.2MnO3 as cathodes for solid oxide fuel cells

    Sacanell J., Sánchez J.H., Rubio Lopez A.E., Martinelli H., Siepe J., Leyva A.G., Ferrari V.P., Pruneda M., Juan D., Lamas D.G. ECS Transactions; 78 (1): 667 - 675. 2017. 10.1149/07801.0667ecst. IF: 0.000

    La0.8Sr0.2MnO3 (LSM) is one of the most commonly used cathodes in Solid Oxide Fuel Cells (SOFC). In spite of the fact that nanostructured cathodes are expected to display improved performance, the high operating temperature (∼ 1000°C) of LSM-based SOFCs hinders their stability. In the present work, we have developed nanostructured cathodes prepared from LSM nanotubes of enhanced performance, allowing its use at lower temperatures (∼ 800°C). We observed that our cathodes have qualitative improvements compared with microstructured materials: firstly, the diffusion in the gas phase is optimized to a negligible level and secondly, evidence of ionic conduction is found, which is extremely rare in LSM cathodes. We propose that this important change in the electrochemical properties is due to the nanostructuration of the cathode and deserves further attention, including the exploration of other materials. © The Electrochemical Society.


  • Enhanced Cooperativity in Supported Spin-Crossover Metal-Organic Frameworks

    Groizard T., Papior N., Le Guennic B., Robert V., Kepenekian M. Journal of Physical Chemistry Letters; 8 (14): 3415 - 3420. 2017. 10.1021/acs.jpclett.7b01248. IF: 9.353

    The impact of surface deposition on cooperativity is explored in Au(111)-supported self-assembled metal-organic frameworks (MOFs) based on Fe(II) ions. Using a thermodynamic model, we first demonstrate that dimensionality reduction combined with deposition on a metal surface is likely to deeply enhance the spin-crossover cooperativity, going from γ3D = 16 K for the bulk material to γ2Dsupp = 386 K for its 2D supported derivative. On the basis of density functional theory, we then elucidate the electronic structure of a promising Fe-based MOF. A chemical strategy is proposed to turn a weakly interacting magnetic system into a strongly cooperative spin-crossover monolayer with γMOFAu(111) = 83 K. These results open a promising route to the fabrication of cooperative materials based on SCO Fe(II) platforms. © 2017 American Chemical Society.


  • Field Effect in Graphene-Based van der Waals Heterostructures: Stacking Sequence Matters

    Stradi D., Papior N.R., Hansen O., Brandbyge M. Nano Letters; 17 (4): 2660 - 2666. 2017. 10.1021/acs.nanolett.7b00473. IF: 12.712

    Stacked van der Waals (vdW) heterostructures where semiconducting two-dimensional (2D) materials are contacted by overlaid graphene electrodes enable atomically thin, flexible electronics. We use first-principles quantum transport simulations of graphene-contacted MoS2 devices to show how the transistor effect critically depends on the stacking configuration relative to the gate electrode. We can trace this behavior to the stacking-dependent response of the contact region to the capacitive electric field induced by the gate. The contact resistance is a central parameter and our observation establishes an important design rule for ultrathin devices based on 2D atomic crystals. © 2017 American Chemical Society.


  • Graphene-based synthetic antiferromagnets and ferrimagnets

    Gargiani P., Cuadrado R., Vasili H.B., Pruneda M., Valvidares M. Nature Communications; 8 (1, 699) 2017. 10.1038/s41467-017-00825-9. IF: 12.124

    Graphene-spaced magnetic systems with antiferromagnetic exchange-coupling offer exciting opportunities for emerging technologies. Unfortunately, the in-plane graphene-mediated exchange-coupling found so far is not appropriate for realistic exploitation, due to being weak, being of complex nature, or requiring low temperatures. Here we establish that ultra-thin Fe/graphene/Co films grown on Ir(111) exhibit robust perpendicular antiferromagnetic exchange-coupling, and gather a collection of magnetic properties well-suited for applications. Remarkably, the observed exchange coupling is thermally stable above room temperature, strong but field controllable, and occurs in perpendicular orientation with opposite remanent layer magnetizations. Atomistic first-principles simulations provide further ground for the feasibility of graphene-spaced antiferromagnetic coupled structures, confirming graphene's direct role in sustaining antiferromagnetic superexchange-coupling between the magnetic films. These results provide a path for the realization of graphene-based perpendicular synthetic antiferromagnetic systems, which seem exciting for fundamental nanoscience or potential use in spintronic devices. © 2017 The Author(s).


  • Growth of Twin-Free and Low-Doped Topological Insulators on BaF2(111)

    Bonell F., Cuxart M.G., Song K., Robles R., Ordejón P., Roche S., Mugarza A., Valenzuela S.O. Crystal Growth and Design; 17 (9): 4655 - 4660. 2017. 10.1021/acs.cgd.7b00525. IF: 4.055

    We demonstrate the growth of twin-free Bi2Te3 and Sb2Te3 topological insulators by molecular beam epitaxy and a sizable reduction of the twin density in Bi2Se3 on lattice-matched BaF2(111) substrates. Using X-ray diffraction, electron diffraction and atomic force microscopy, we systematically investigate the parameters influencing the formation of twin domains and the morphology of the films, and show that Se- and Te-based alloys differ by their growth mechanism. Optimum growth parameters are shown to result in intrinsically low-doped films, as probed by angle-resolved photoelectron spectroscopy. In contrast to previous approaches in which twin-free Bi2Se3 films are achieved by increasing the substrate roughness, the quality of our Bi2Te3 is superior on the flattest BaF2 substrates. This finding indicates that, during nucleation, the films not only interact with the topmost atomic substrate layer but also with buried layers that provide the necessary stacking information to promote a single twin, an observation that is supported by ab initio calculations. © 2017 American Chemical Society.


  • Hydrogen Activation by Frustrated Lewis Pairs Revisited by Metadynamics Simulations

    Liu L., Lukose B., Ensing B. Journal of Physical Chemistry C; 121 (4): 2046 - 2051. 2017. 10.1021/acs.jpcc.6b09991. IF: 4.536

    Frustrated Lewis pairs have great potential as metal-free catalysts, for example, for the activation of molecular hydrogen. However, rational design of improved catalysts is hampered because the catalytic reaction mechanisms still remain largely unclear. In this study, we present a density-functional-theory-based metadynamics study of the hydrogen activation by a typical frustrated Lewis pair, tBu3P/B(C6F5)3. The computed free-energy landscape reveals a different reaction path compared with the ones in the literature. Importantly, we found different roles of the Lewis acid and base centers in the hydrogen activation. The rate-determining step is the hydride transfer to the Lewis acid, and the overall reaction is found to be exothermic once the proton transfer to the Lewis base step is accomplished. © 2017 American Chemical Society.


  • Multiscale modeling of spin transport across a diffuse interface

    Chureemart J., Cuadrado R., Chureemart P., Chantrell R.W. Journal of Magnetism and Magnetic Materials; 443: 287 - 292. 2017. 10.1016/j.jmmm.2017.07.085. IF: 2.630

    We present multiscale calculations to describe the spin transport behavior of the Co/Cu bilayer structure including the effect of the interface. The multiscale approach introduces the connection between the ab initio calculation used to describe the electronic structure of the system and the generalized spin accumulation model employed to describe the spin transport behavior. We have applied our model to atomically smooth and diffuse interfaces. The results demonstrate the huge importance of the use of first principle calculations, not only due to the interfacial coordinates optimization but also the magnetic and electronic properties obtained through the electronic structure. The system including the effect of interface with and without the charge fluctuation are studied. The results indicate that changes of electronic structure at the Co/Cu interface give rise to an interfacial resistance distributed over several atomic planes, similar to the effect of interface diffusion. We argue that even atomically smooth Co/Cu interfaces have properties analogous to a diffuse interface due to the variation of electronic structure at the interface. © 2017 The Authors


  • Oxygen Reduction Mechanisms in Nanostructured La0.8Sr0.2MnO3 Cathodes for Solid Oxide Fuel Cells

    Sacanell J., Hernández Sánchez J., Rubio López A.E., Martinelli H., Siepe J., Leyva A.G., Ferrari V., Juan D., Pruneda M., Mejía Gómez A., Lamas D.G. Journal of Physical Chemistry C; 121 (12): 6533 - 6539. 2017. 10.1021/acs.jpcc.7b00627. IF: 4.536

    In this work we outline the mechanisms contributing to the oxygen reduction reaction in nanostructured cathodes of La0.8Sr0.2MnO3 (LSM) for Solid Oxide Fuel Cells (SOFC). These cathodes, developed from LSM nanostructured tubes, can be used at lower temperatures compared to microstructured ones, and this is a crucial fact to avoid the degradation of the fuel cell components. This reduction of the operating temperatures stems mainly from two factors: (i) the appearance of significant oxide ion diffusion through the cathode material in which the nanostructure plays a key role and (ii) an optimized gas phase diffusion of oxygen through the porous structure of the cathode, which becomes negligible. A detailed analysis of our Electrochemical Impedance Spectroscopy supported by first-principles calculations point toward an improved overall cathodic performance driven by a fast transport of oxide ions through the cathode surface. (Figure Presented). © 2017 American Chemical Society.


  • Voltage-Induced Coercivity Reduction in Nanoporous Alloy Films: A Boost toward Energy-Efficient Magnetic Actuation

    Quintana A., Zhang J., Isarain-Chávez E., Menéndez E., Cuadrado R., Robles R., Baró M.D., Guerrero M., Pané S., Nelson B.J., Müller C.M., Ordejón P., Nogués J., Pellicer E., Sort J. Advanced Functional Materials; 27 (32, 1701904) 2017. 10.1002/adfm.201701904. IF: 12.124

    Magnetic data storage and magnetically actuated devices are conventionally controlled by magnetic fields generated using electric currents. This involves significant power dissipation by Joule heating effect. To optimize energy efficiency, manipulation of magnetic information with lower magnetic fields (i.e., lower electric currents) is desirable. This can be accomplished by reducing the coercivity of the actuated material. Here, a drastic reduction of coercivity is observed at room temperature in thick (≈600 nm), nanoporous, electrodeposited Cu–Ni films by simply subjecting them to the action of an electric field. The effect is due to voltage-induced changes in the magnetic anisotropy. The large surface-area-to-volume ratio and the ultranarrow pore walls of the system allow the whole film, and not only the topmost surface, to effectively contribute to the observed magnetoelectric effect. This waives the stringent “ultrathin-film requirement” from previous studies, where small voltage-driven coercivity variations were reported. This observation expands the already wide range of applications of nanoporous materials (hitherto in areas like energy storage or catalysis) and it opens new paradigms in the fields of spintronics, computation, and magnetic actuation in general. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • What Controls Photocatalytic Water Oxidation on Rutile TiO2(110) under Ultra-High-Vacuum Conditions?

    Migani A., Blancafort L. Journal of the American Chemical Society; 139 (34): 11845 - 11856. 2017. 10.1021/jacs.7b05121. IF: 13.858

    The photocatalytic O-H dissociation of water absorbed on a rutile TiO2(110) surface in ultrahigh vacuum (UHV) is studied with spin-polarized density functional theory and a hybrid exchange-correlation functional (HSE06), treating the excited-state species as excitons with triplet multiplicity. This system is a model for the photocatalytic oxidation of water by TiO2 in an aqueous medium, which is relevant for the oxygen evolution reaction and photodegradation of organic pollutants. We provide a comprehensive mechanistic picture where the most representative paths correspond to excitonic configurations with the hole located on three- and two-coordinate surface oxygen atoms (O3s and O2s). Our picture explains the formation of the species observed experimentally. At near band gap excitation, the O3s path leads to the generation of hydroxyl anions which diffuse on the surface, without net oxidation. In contrast, free hydroxyl radicals are formed at supra band gap excitation (e.g., 266 nm) from an interfacial exciton that undergoes O-H dissociation. The oxidation efficiency is low because the path associated with the O2s exciton, which is the most favored one thermodynamically, is unreactive because of a high propensity for charge recombination. Our results are also relevant to understand the reactivity in the liquid phase. We assign the photoluminescence measured for atomically flat TiO2(110) surfaces in an aqueous medium to the O3s exciton, in line with the proposal based on experiments, and we have identified a species derived from the O2s exciton with an activated O2s-Ti bond that may be relevant in photocatalytic applications in an aqueous medium. © 2017 American Chemical Society.


2016

  • AFM Imaging of Mercaptobenzoic Acid on Au(110): Submolecular Contrast with Metal Tips

    Hauptmann N., Robles R., Abufager P., Lorente N., Berndt R. Journal of Physical Chemistry Letters; 7 (11): 1984 - 1990. 2016. 10.1021/acs.jpclett.6b00684. IF: 8.539

    A self-assembled monolayer of mercaptobenzoic acid (MBA) on Au(110) is investigated with scanning tunneling and atomic force microscopy (STM and AFM) and density functional calculations. High-resolution AFM images obtained with metallic tips show clear contrasts between oxygen atoms and phenyl moieties. The contrast above the oxygen atoms is due to attractive covalent interactions, which is different than previously reported high-resolution images, where Pauli repulsion dominated the image contrast. We show that the bonding of MBA to the substrate occurs mainly through dispersion interactions, whereas the thiol-Au bond contributes only a quarter of the adsorption energy. No indication of Au adatoms mediating the thiol-Au interaction was found in contrast to other thiol-bonded systems. However, MBA lifts the Au(110)-(2 × 1) reconstruction. © 2016 American Chemical Society.


  • Effect of asymmetric concentration profile on thermal conductivity in Ge/SiGe superlattices

    Hahn K.R., Cecchi S., Colombo L. Applied Physics Letters; 108 (20, 203102) 2016. 10.1063/1.4949491. IF: 3.142

    The effect of the chemical composition in Si/Ge-based superlattices on their thermal conductivity has been investigated using molecular dynamics simulations. Simulation cells of Ge/SiGe superlattices have been generated with different concentration profiles such that the Si concentration follows a step-like, a tooth-saw, a Gaussian, and a gamma-type function in direction of the heat flux. The step-like and tooth-saw profiles mimic ideally sharp interfaces, whereas Gaussian and gamma-type profiles are smooth functions imitating atomic diffusion at the interface as obtained experimentally. Symmetry effects have been investigated comparing the symmetric profiles of the step-like and the Gaussian function to the asymmetric profiles of the tooth-saw and the gamma-type function. At longer sample length and similar degree of interdiffusion, the thermal conductivity is found to be lower in asymmetric profiles. Furthermore, it is found that with smooth concentration profiles where atomic diffusion at the interface takes place the thermal conductivity is higher compared to systems with atomically sharp concentration profiles. © 2016 Author(s).


  • Electronic structure of 2H-NbSe2 single-layers in the CDW state

    Silva-Guillén J.Á., Ordejón P., Guinea F., Canadell E. 2D Materials; 3 (3, 035028) 2016. 10.1088/2053-1583/3/3/035028. IF: 9.611

    Adensity functional theory study of NbSe2"Qsingle-layers in the normal non-modulated and the 3"Q¡Ñ"Q3 CDWstates is reported.Weshow that, in the single layer, the CDW barely affects the Fermi surface of the system, thus ruling out a nesting mechanism as the driving force for the modulation. The CDW stabilizes levels lying around 1.35 eV below the Fermi level within the Se-based valence band but having a substantial Nb-VNb bonding character. The absence of interlayer interactions leads to the suppression of the pancake-like portion of the bulk Fermi surface in the single-layer.Weperform scanning tunneling microscopy simulations and find that the images noticeably change with the sign and magnitude of the voltage bias. The atomic corrugation of the Se sublayer induced by the modulation plays a primary role in leading to these images, but the electronic reorganization also has an important contribution. The analysis of the variation of these images with the bias voltage does not support a Fermi surface nesting mechanism for the CDW. It is also shown that underlying graphene layers (present in some of the recent experimental work) do not modify the conduction band, but do affect the shape of the valence band of NbSe2"Qsingle-layers. The relevance of these results in understanding recent physical measurements for NbSe2"Qsingle-layers is discussed. © 2016 IOP Publishing Ltd.


  • Following the steps of a reaction by direct imaging of many individual molecules

    Van Vörden D., Wortmann B., Schmidt N., Lange M., Robles R., Brendel L., Bobisch C.A., Möller R. Chemical Communications; 52 (49): 7711 - 7714. 2016. 10.1039/c6cc02959k. IF: 6.567

    The dehydrogenation and dechlorination of FeOEP-Cl on Cu(111) has been studied in detail by scanning tunneling microscopy. Although, it is not possible to follow the reaction of an individual molecule, the complete pathway of the reaction with 22 inequivalent intermediate states and the rates of the involved processes are revealed. This is achieved by combining the analysis of a large data set showing thousands of molecules in the different stages of the reaction with numerical simulations. © 2016 The Royal Society of Chemistry.


  • Heat transport through a solid-solid junction: The interface as an autonomous thermodynamic system

    Rurali R., Colombo L., Cartoixà X., >Øivind W., Trinh T.T., Bedeaux D., Kjelstrup S. Physical Chemistry Chemical Physics; 18 (20): 13741 - 13745. 2016. 10.1039/c6cp01872f. IF: 4.449

    We perform computational experiments using nonequilibrium molecular dynamics simulations, showing that the interface between two solid materials can be described as an autonomous thermodynamic system. We verify the local equilibrium and give support to the Gibbs description of the interface also away from the global equilibrium. In doing so, we reconcile the common formulation of the thermal boundary resistance as the ratio between the temperature discontinuity at the interface and the heat flux with a more rigorous derivation from nonequilibrium thermodynamics. We also show that thermal boundary resistance of a junction between two pure solid materials can be regarded as an interface property, depending solely on the interface temperature, as implicitly assumed in some widely used continuum models, such as the acoustic mismatch model. Thermal rectification can be understood on the basis of different interface temperatures for the two flow directions. © The Owner Societies 2016.


  • How disorder affects topological surface states in the limit of ultrathin Bi2Se3 films

    Song K., Soriano D., Robles R., Ordejon P., Roche S. 2D Materials; 3 (4, 045007) 2016. 10.1088/2053-1583/3/4/045007. IF: 9.611

    We present a first-principles study of electronic properties of ultrathin films of topological insulators (TIs) and scrutinize the role of disorder on the robustness of topological surface states, which can be analysed through their spin textures. The presence of twin grain boundaries is found to increase the band gap of the film, while preserving the spin texture of states in first conduction and valence bands. Differently, partial hydrogenation of one surface not only results in some self-doping effect, but also provokes some alteration of the spin texture symmetry of the electronic states. The formation of a new Dirac cone at M-point of the Brillouin zone of the hydrogenated surface, together with a modified spin texture characteristics are consistent with a dominant Dresselhaus spin-orbit interaction type, more usually observed in 3D materials. Our findings indicate that defects can either be detrimental or beneficial for exploring spin transport of surface states in the limit of ultrathin films of TIs, which maximizes surface over bulk phenomena. © 2016 IOP Publishing Ltd.


  • In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe1- yMnyPt-L10 bulk alloy

    Cuadrado R., Liu K., Klemmer T.J., Chantrell R.W. Applied Physics Letters; 108 (12, 123102) 2016. 10.1063/1.4944534. IF: 3.142

    The random substitution of a non-magnetic species instead of Fe atoms in FePt-L10 bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe1- yMnyPt-L10 (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L10 bulk due to this lattice variation leading to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell. © 2016 AIP Publishing LLC.


  • Nanotexturing to Enhance Photoluminescent Response of Atomically Thin Indium Selenide with Highly Tunable Band Gap

    Brotons-Gisbert M., Andres-Penares D., Suh J., Hidalgo F., Abargues R., Rodríguez-Cantó P.J., Segura A., Cros A., Tobias G., Canadell E., Ordejón P., Wu J., Martínez-Pastor J.P., Sánchez-Royo J.F. Nano Letters; 16 (5): 3221 - 3229. 2016. 10.1021/acs.nanolett.6b00689. IF: 13.779

    Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density. © 2016 American Chemical Society.


  • Noncontact atomic force microscopy and density functional theory studies of the (2×2) reconstructions of the polar AlN(0001) surface

    Chaumeton F., Robles R., Pruneda M., Lorente N., Eydoux B., Bouju X., Gauthier S., Martrou D. Physical Review B; 94 (16, 165305) 2016. 10.1103/PhysRevB.94.165305.

    Combined experimental and theoretical studies permit us to determine new protocols for growing by molecular beam epitaxy the technologically interesting N-rich aluminum nitride (AlN) surfaces. This is achieved by dosing the precursor gases at unusually low rates. With the help of calculated structures by using density functional theory and Boltzmann distribution of the reconstructed cells, we proposed to assign the measured surface obtained with a growth rate of 10 nm/h to a (2×2) reconstructed surface involving one additional N atom per unit cell. These N-rich AlN surfaces could open new routes to dope AlN layers with important implications in high-power and temperature technological applications. © 2016 American Physical Society.


  • On-Surface Engineering of a Magnetic Organometallic Nanowire

    Ormaza M., Robles R., Bachellier N., Abufager P., Lorente N., Limot L. Nano Letters; 16 (1): 588 - 593. 2016. 10.1021/acs.nanolett.5b04280. IF: 13.779

    The manipulation of the molecular spin state by atom doping is an attractive strategy to confer desirable magnetic properties to molecules. Here, we present the formation of novel magnetic metallocenes by following this approach. In particular, two different on-surface procedures to build isolated and layer-integrated Co-ferrocene (CoFc) molecules on a metallic substrate via atomic manipulation and atom deposition are shown. The structure as well as the electronic properties of the so-formed molecule are investigated combining scanning tunneling microscopy and spectroscopy with density functional theory calculations. It is found that unlike single ferrocene a CoFc molecule possesses a magnetic moment as revealed by the Kondo effect. These results correspond to the first controlled procedure toward the development of tailored metallocene-based nanowires with a desired chemical composition, which are predicted to be promising materials for molecular spintronics. © 2015 American Chemical Society.


  • Optical Absorption Spectra and Excitons of Dye-Substrate Interfaces: Catechol on TiO2(110)

    Mowbray D.J., Migani A. Journal of Chemical Theory and Computation; 12 (6): 2843 - 2852. 2016. 10.1021/acs.jctc.6b00217. IF: 5.301

    Optimizing the photovoltaic efficiency of dye-sensitized solar cells (DSSC) based on staggered gap heterojunctions requires a detailed understanding of sub-band gap transitions in the visible from the dye directly to the substrate's conduction band (CB) (type-II DSSCs). Here, we calculate the optical absorption spectra and spatial distribution of bright excitons in the visible region for a prototypical DSSC, catechol on rutile TiO2(110), as a function of coverage and deprotonation of the OH anchoring groups. This is accomplished by solving the Bethe-Salpeter equation (BSE) based on hybrid range-separated exchange and correlation functional (HSE06) density functional theory (DFT) calculations. Such a treatment is necessary to accurately describe the interfacial level alignment and the weakly bound charge transfer transitions that are the dominant absorption mechanism in type-II DSSCs. Our HSE06 BSE spectra agree semiquantitatively with spectra measured for catechol on anatase TiO2 nanoparticles. Our results suggest deprotonation of catechol's OH anchoring groups, while being nearly isoenergetic at high coverages, shifts the onset of the absorption spectra to lower energies, with a concomitant increase in photovoltaic efficiency. Further, the most relevant bright excitons in the visible region are rather intense charge transfer transitions with the electron and hole spatially separated in both the [110] and [001] directions. Such detailed information on the absorption spectra and excitons is only accessible via periodic models of the combined dye-substrate interface. © 2016 American Chemical Society.


  • Reversible 2D Phase Transition Driven by an Electric Field: Visualization and Control on the Atomic Scale

    Wortmann B., Vörden D.V., Graf P., Robles R., Abufager P., Lorente N., Bobisch C.A., Möller R. Nano Letters; 16 (1): 528 - 533. 2016. 10.1021/acs.nanolett.5b04174. IF: 13.779

    We report on a reversible structural phase transition of a two-dimensional system that can be locally induced by an external electric field. Two different structural configurations may coexist within a CO monolayer on Cu(111). The balance between the two phases can be shifted by an external electric field, causing the domain boundaries to move, increasing the area of the favored phase controllable both in location and size. If the field is further enhanced new domains nucleate. The arrangement of the CO molecules on the Cu surface is observed in real time and real space with atomic resolution while the electric field driving the phase transition is easily varied over a broad range. Together with the well-known molecular manipulation of CO adlayers, our findings open exciting prospects for combining spontaneous long-range order with man-made CO structures such as "molecule cascades" or "molecular graphene". Our new manipulation mode permits us to bridge the gap between fundamental concepts and the fabrication of arbitrary atomic patterns in large scale, by providing unprecedented insight into the physics of structural phase transitions on the atomic scale. © 2015 American Chemical Society.


  • Spin-polarised edge states in atomic Mn chains supported on Cu2N/Cu (100)

    Choi D.-J., Robles R., Gauyacq J.-P., Rubio-Verdú C., Lorente N., Ignacio Pascual J. Journal of Physics Condensed Matter; 28 (23, 23LT01) 2016. 10.1088/0953-8984/28/23/23LT01. IF: 2.209

    Scanning tunnelling microscopy and density functional theory studies of manganese chains adsorbed on Cu2N/Cu (100) reveal an unsuspected electronic edge state at ∼ 1 eV above the Fermi energy. This Tamm-like state is strongly localised to the terminal Mn atoms of the chain and fully spin polarised. However, no equivalence is found for occupied states, and the electronic structure at ∼ -1 eV is mainly spin unpolarised due to the extended p-states of the N atoms that mediate the coupling between the Mn atoms in the chain. The spin polarisation of the edge state is affected by the antiferromagnetic ordering of the chains leading to non-trivial consequences. © 2016 IOP Publishing Ltd.


  • Structural and magnetic properties of FeMnx chains (x=1-6) supported on Cu2 N/Cu (100)

    Choi D.-J., Robles R., Gauyacq J.-P., Ternes M., Loth S., Lorente N. Physical Review B; 94 (8, 085406) 2016. 10.1103/PhysRevB.94.085406.

    Heterogeneous atomic magnetic chains are built by atom manipulation on a Cu2N/Cu (100) substrate. Their magnetic properties are studied and rationalized by a combined scanning tunneling microscopy (STM) and density functional theory (DFT) work completed by model Hamiltonian studies. The chains are built using Fe and Mn atoms ontop of the Cu atoms along the N rows of the Cu2N surface. Here, we present results for FeMnx chains (x=1-6) emphasizing the evolution of the geometrical, electronic, and magnetic properties with chain size. By fitting our results to a Heisenberg Hamiltonian we have studied the exchange-coupling matrix elements J for different chains. For the shorter chains, x≤2, we have included spin-orbit effects in the DFT calculations, extracting the magnetic anisotropy energy. Our results are also fitted to a simple anisotropic spin Hamiltonian and we have extracted values for the longitudinal-anisotropy D and transversal-anisotropy E constants. These parameters together with the values for J allow us to compute the magnetic excitation energies of the system and to compare them with the experimental data. © 2016 American Physical Society.


  • Surface cis Effect: Influence of an Axial Ligand on Molecular Self-Assembly

    Knaak T., Gopakumar T.G., Schwager B., Tuczek F., Robles R., Lorente N., Berndt R. Journal of the American Chemical Society; 138 (24): 7544 - 7550. 2016. 10.1021/jacs.6b03710. IF: 13.038

    Adding ligands to molecules can have drastic and unforeseen consequences in the final products of a reaction. Recently a surface trans effect due to the weakening of a molecule-surface bond was reported. Here, we show a surface cis effect where an axial ligand at adsorbed transition-metal complexes enables lateral bonding among the molecules. In the absence of this ligand, the intermolecular interaction is repulsive and supramolecular patterns are not observed. Fe-tetramethyl-tetraazaannulene on Au(111) was investigated using low-temperature scanning tunneling microscopy and spectroscopy along with density functional theory calculations. At low coverages, the molecules remain isolated. Exposure to CO leads to axial CO bonding and induces reordering into extended clusters of chiral molecular trimers. The changed self-assembly pattern is due to a CO-induced modification of the molecular structure and the corresponding charge transfer between the molecule and the substrate, which in turn changes the lateral intermolecular forces. © 2016 American Chemical Society.


  • Theoretical studies of Rashba and Dresselhaus effects in hybrid organic-inorganic perovskites for optoelectronic applications

    Pedesseau L., Kepenekian M., Robles R., Sapori D., Katan C., Even J. Proceedings of SPIE - The International Society for Optical Engineering; 9742 ( 97421B) 2016. 10.1117/12.2213618. IF: 0.000

    In this paper, we propose a description of the Rashba-Dresselhaus effect in Hybrid Organic Perovskite (HOP). We show how the loss of the inversion symmetry leads to the loss of the spin degeneracy. An example of structure where both Rashba and Dresselhaus operate is illustrated with the formamidinium tin iodide CH(NH2)2SnI3. The control of this effect is as well addressed by two examples. A first example concerns the control with the temperature and is demonstrated for the 2D HOP Bz2PbCl4 (Bz = benzylammonium). Then the control with an external field is established for the 3D HOP CH3NH3PbBr3. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.


  • Thermal conductivity of MoS2 polycrystalline nanomembranes

    Sledzinska M., Graczykowski B., Placidi M., Reig D.S., El Sachat A., Reparaz J.S., Alzina F., Mortazavi B., Quey R., Colombo L., Roche S., Torres C.M.S. 2D Materials; 3 (3, 035016) 2016. 10.1088/2053-1583/3/3/035016. IF: 9.611

    Heat conduction in 2D materials can be effectively engineered by means of controlling nanoscale grain structure. Afavorable thermal performance makes these structures excellent candidates for integrated heat management units. Here we show combined experimental and theoretical studies for MoS2 nanosheets in a nanoscale grain-size limit.Wereport thermal conductivity measurements on 5 nm thick polycrystalline MoS2 by means of 2-laser Raman thermometry. The free-standing, drum-like MoS2 nanomembranes were fabricated using a novel polymer- and residue-free, wet transfer, in which we took advantage of the difference in the surface energies between MoS2 and the growth substrate to transfer the CVD-grown nanosheets. The measurements revealed a strong reduction in the in-plane thermal conductivity down to about 0.73 ± 0.25 W m-1 K-1. The results are discussed theoretically using finite elements method simulations for a polycrystalline film, and a scaling trend of the thermally conductivity with grain size is proposed. © 2016 IOP Publishing Ltd.


  • Thermal rectification in silicon by a graded distribution of defects

    Dettori R., Melis C., Rurali R., Colombo L. Journal of Applied Physics; 119 (21, 215102) 2016. 10.1063/1.4953142. IF: 2.101

    We discuss about computer experiments based on nonequilibrium molecular dynamics simulations providing evidence that thermal rectification can be obtained in bulk Si by a non-uniform distribution of defects. We consider a graded population of both Ge substitutional defects and nanovoids, distributed along the direction of an applied thermal bias, and predict a rectification factor comparable to what is observed in other low-dimensional Si-based nanostructures. By considering several defect distribution profiles, thermal bias conditions, and sample sizes, the present results suggest that a possible way for tuning the thermal rectification is by defect engineering. © 2016 Author(s).


  • Thermal transport in porous Si nanowires from approach-to-equilibrium molecular dynamics calculations

    Cartoixà X., Dettori R., Melis C., Colombo L., Rurali R. Applied Physics Letters; 109 (1, 013107) 2016. 10.1063/1.4955038. IF: 3.142

    We study thermal transport in porous Si nanowires (SiNWs) by means of approach-to-equilibrium molecular dynamics simulations. We show that the presence of pores greatly reduces the thermal conductivity, κ, of the SiNWs as long mean free path phonons are suppressed. We address explicitly the dependence of κ on different features of the pore topology - such as the porosity and the pore diameter - and on the nanowire (NW) geometry - diameter and length. We use the results of the molecular dynamics calculations to tune an effective model, which is capable of capturing the dependence of κ on porosity and NW diameter. The model illustrates the failure of Matthiessen's rule to describe the coupling between boundary and pore scattering, which we account for by the inclusion of an additional empirical term. © 2016 Author(s).


2015

  • Assembly of ferrocene molecules on metal surfaces revisited

    Ormaza M., Abufager P., Bachellier N., Robles R., Verot M., Le Bahers T., Bocquet M.-L., Lorente N., Limot L. Journal of Physical Chemistry Letters; 6 (3): 395 - 400. 2015. 10.1021/jz5026118. IF: 7.458

    Metallocene (MCp2) wires have recently attracted considerable interest in relation to molecular spintronics due to predictions concerning their half-metallic nature. This exciting prospect is however hampered by the little and often-contradictory knowledge we have concerning the metallocene self-assembly and interaction with a metal. Here, we elucidate these aspects by focusing on the adsorption of ferrocene on Cu(111) and Cu(100). Combining low-temperature scanning tunneling microscopy and density functional theory calculations, we demonstrate that the two-dimensional molecular arrangement consists of vertical- and horizontal-lying molecules. The noncovalent T-shaped interactions between Cp rings of vertical and horizontal molecules are essential for the stability of the physisorbed molecular layer. These results provide a fresh insight into ferrocene adsorption on surfaces and may serve as an archetypal reference for future work with this important variety of organometallic molecules. (Figure Presented). © 2015 American Chemical Society.


  • Capacitive DNA Detection Driven by Electronic Charge Fluctuations in a Graphene Nanopore

    Feliciano G.T., Sanz-Navarro C., Coutinho-Neto M.D., Ordejón P., Scheicher R.H., Rocha A.R. Physical Review Applied; 3 (3, 034003) 2015. 10.1103/PhysRevApplied.3.034003. IF: 0.000

    The advent of parallelized automated methods for rapid whole-genome analysis has led to an exponential drop in costs, thus greatly accelerating biomedical research and discovery. Third-generation sequencing techniques, which would utilize the characteristic electrical conductance of the four different nucleotides, could facilitate longer base read lengths and an even lower price per genome. In this work, we propose and apply a quantum-classical hybrid methodology to quantitatively determine the influence of the solvent on the dynamics of DNA and the resulting electron transport properties of a prototypic sequencing device utilizing a graphene nanopore through which the nucleic-acid chain is threaded. Our results show that charge fluctuations in the nucleotides are responsible for characteristic conductance modulations in this system, which can be regarded as a field-effect transistor tuned by the dynamic aqueous environment. © 2015 American Physical Society.


  • Comparing Quasiparticle H2O Level Alignment on Anatase and Rutile TiO2

    Sun H., Mowbray D.J., Migani A., Zhao J., Petek H., Rubio A. ACS Catalysis; 5 (7): 4242 - 4254. 2015. 10.1021/acscatal.5b00529. IF: 9.312

    Knowledge of the alignment of molecular frontier levels in the ground state can be used to predict the photocatalytic activity of an interface. The position of the adsorbate's highest occupied molecular orbital (HOMO) levels relative to the substrate's valence band maximum (VBM) in the interface describes the favorability of photogenerated hole transfer from the VBM to the adsorbed molecule. This is a key quantity for assessing and comparing H2O photooxidation activities on two prototypical photocatalytic TiO2 surfaces: anatase (A)-TiO2(101) and rutile (R)-TiO2(110). Using the projected density of states (DOS) from state-of-the-art quasiparticle (QP) G0W0 calculations, we assess the relative photocatalytic activity of intact and dissociated H2O on coordinately unsaturated (Ticus) sites of idealized stoichiometric A-TiO2(101)/R-TiO2(110) and bridging O vacancies (Obrvac) of defective A-TiO2-x(101)/R-TiO2-x(110) surfaces (x = 1/4, 1/8) for various coverages. Such a many-body treatment is necessary to correctly describe the anisotropic screening of electron-electron interactions at a photocatalytic interface and, hence, obtain accurate interfacial level alignments. The more favorable ground state HOMO level alignment for A-TiO2(101) may explain why the anatase polymorph shows higher photocatalytic activities than the rutile polymorph. Our results indicate that (1) hole trapping is more favored on A-TiO2(101) than R-TiO2(110) and (2) HO@Ticus is more photocatalytically active than intact H2O@Ticus. © 2015 American Chemical Society.


  • Electromechanical response at polar zigzag boundaries in hybrid monolayers

    Martinez-Gordillo R., Pruneda M. Physical Review B - Condensed Matter and Materials Physics; 91 (4, 045411) 2015. 10.1103/PhysRevB.91.045411. IF: 3.736

    First-principles calculations are used to demonstrate electromechanical control of charge and spin at zigzag-edged interfaces between graphene and boron-nitride domains in hybrid monolayers. We show how, through a direct piezoelectric effect, the interfacial bound charges and associated electric fields can be tuned by application of an external mechanical force (stress) on the system. This results in mechanical control of the edge magnetization (piezomagnetic effect), and the possibility to transform a semiconducting heterostructure into a half-metal. The inverse effect (application of an external electric field to induce a mechanical deformation) goes together with a magnetoelectric response, which under ideal conditions we estimate to be comparable to that of prototypical Cr2O3. These effects originate from the magnetic properties of graphene's zigzag edges and the dielectric properties of the boron-nitride domain, and can also be expected in any other coplanar heterostructures with polar discontinuities. © 2015 American Physical Society.


  • FeCoCp3 Molecular Magnets as Spin Filters

    Abufager P.N., Robles R., Lorente N. Journal of Physical Chemistry C; 119 (22): 12119 - 12129. 2015. 10.1021/acs.jpcc.5b01839. IF: 4.772

    Metallorganic molecules have been proposed as excellent spin filters in molecular spintronics because of the large spin polarization of their electronic structure. However, most of the studies involving spin transport have disregarded fundamental aspects such as the magnetic anisotropy of the molecule and the excitation of spin-flip processes during electron transport. Here, we study a molecule containing a Co and an Fe atom stacked between three cyclopentadienyl rings, which presents a large magnetic anisotropy and a S = 1. These figures are superior to other molecules with the same transition metal and improves the spin-filtering capacities of the molecule. Nonequilibrium Green's functions calculations based on density functional theory predict excellent spin-filtering properties both in tunnel and contact transport regimes. However, exciting the first magnetic state drastically reduces the current's spin polarization. Furthermore, a difference of temperature between electrodes leads to strong thermoelectric effects that also suppress spin polarization. Our study shows that in principle good molecular candidates for spintronics need to be confronted with inelastic and thermoelectric effects. (Graph Presented). © 2015 American Chemical Society.


  • Polar discontinuities and 1D interfaces in monolayered materials

    Martinez-Gordillo R., Pruneda M. Progress in Surface Science; 90 (4): 444 - 463. 2015. 10.1016/j.progsurf.2015.08.001. IF: 5.696

    Interfaces are the birthplace of a multitude of fascinating discoveries in fundamental science, and have enabled modern electronic devices, from transistors, to lasers, capacitors or solar cells. These interfaces between bulk materials are always bi-dimensional (2D) 'surfaces'. However the advent of graphene and other 2D crystals opened up a world of possibilities, as in this case the interfaces become one-dimensional (1D) lines. Although the properties of 1D nanoribbons have been extensively discussed in the last few years, 1D interfaces within infinite 2D systems had remained mostly unexplored until very recently. These include grain boundaries in polycrystalline samples, or interfaces in hybrid 2D sheets composed by segregated domains of different materials (as for example graphene/BN hybrids, or chemically different transition metal dichalcogenides). As for their 2D counterparts, some of these 1D interfaces exhibit polar characteristics, and can give rise to fascinating new physical properties. Here, recent experimental discoveries and theoretical predictions on the polar discontinuities that arise at these 1D interfaces will be reviewed, and the perspectives of this new research topic, discussed. © 2015 Elsevier Ltd. All rights reserved.


  • Quasiparticle interfacial level alignment of highly hybridized frontier levels: H2O on TiO2(110)

    Migani A., Mowbray D.J., Zhao J., Petek H. Journal of Chemical Theory and Computation; 11 (1): 239 - 251. 2015. 10.1021/ct500779s. IF: 5.498

    Knowledge of the frontier levels' alignment prior to photoirradiation is necessary to achieve a complete quantitative description of H2O photocatalysis on TiO2(110). Although H2O on rutile TiO2(110) has been thoroughly studied both experimentally and theoretically, a quantitative value for the energy of the highest H2O occupied levels is still lacking. For experiment, this is due to the H2O levels being obscured by hybridization with TiO2(110) levels in the difference spectra obtained via ultraviolet photoemission spectroscopy (UPS). For theory, this is due to inherent difficulties in properly describing many-body effects at the H2O-TiO2(110) interface. Using the projected density of states (DOS) from state-of-the-art quasiparticle (QP) G0W0, we disentangle the adsorbate and surface contributions to the complex UPS spectra of H2O on TiO2(110). We perform this separation as a function of H2O coverage and dissociation on stoichiometric and reduced surfaces. Due to hybridization with the TiO2(110) surface, the H2O 3a1 and 1b1 levels are broadened into several peaks between 5 and 1 eV below the TiO2(110) valence band maximum (VBM). These peaks have both intermolecular and interfacial bonding and antibonding character. We find the highest occupied levels of H2O adsorbed intact and dissociated on stoichiometric TiO2(110) are 1.1 and 0.9 eV below the VBM. We also find a similar energy of 1.1 eV for the highest occupied levels of H2O when adsorbed dissociatively on a bridging O vacancy of the reduced surface. In both cases, these energies are significantly higher (by 0.6 to 2.6 eV) than those estimated from UPS difference spectra, which are inconclusive in this energy region. Finally, we apply self-consistent QPGW (scQPGW1) to obtain the ionization potential of the H2O-TiO2(110) interface. (Figure Presented). © 2014 American Chemical Society.


  • Quasiparticle spectra of 2H-NbSe2: Two-band superconductivity and the role of tunneling selectivity

    Noat Y., Silva-Guillén J.A., Cren T., Cherkez V., Brun C., Pons S., Debontridder F., Roditchev D., Sacks W., Cario L., Ordejón P., García A., Canadell E. Physical Review B - Condensed Matter and Materials Physics; 92 (13, 134510) 2015. 10.1103/PhysRevB.92.134510. IF: 3.736

    We have studied the superconducting state of 2H-NbSe2 by scanning tunneling spectroscopy along two different crystal orientations, the c and the a/b axes. Along the c axis a large gap is dominant in the spectra, while a smaller gap is measured along the a/b axis. We show that these spectra are accurately described by the McMillan model where the small gap is induced through the coupling to the band associated with the large gap. In order to assign the small and large gaps to specific parts of the 2H-NbSe2 Fermi surface, the electronic structure was studied using first-principles calculations. While we cannot exclude the possibility of intrinsic anisotropy of the gaps, we propose that the large gap opens in the Fermi surface cylinders located around the corner K points while the sheets located around Γ are associated with the small gap. An additional component of the Fermi surface, a selenium based pocket, plays an essential role in the tunneling process. The role of the charge density wave occurring in this material is also discussed. Finally, we are able to give a coherent description of the observed characteristics of the tunneling spectra of 2H-NbSe2 as well as the differences with 2H-NbS2 where no charge density wave state is present. Further experimental work, such as high-resolution ARPES, would be very useful to confirm our interpretation. The approach and modeling developed here could also be relevant for other compounds of the dichalcogenide family. © 2015 American Physical Society.


  • Rashba and Dresselhaus Effects in Hybrid Organic-Inorganic Perovskites: From Basics to Devices

    Kepenekian M., Robles R., Katan C., Sapori D., Pedesseau L., Even J. ACS Nano; 9 (12): 11557 - 11567. 2015. 10.1021/acsnano.5b04409. IF: 12.881

    We use symmetry analysis, density functional theory calculations, and k·p modeling to scrutinize Rashba and Dresselhaus effects in hybrid organic-inorganic halide perovskites. These perovskites are at the center of a recent revolution in the field of photovoltaics but have also demonstrated potential for optoelectronic applications such as transistors and light emitters. Due to a large spin-orbit coupling of the most frequently used metals, they are also predicted to offer a promising avenue for spin-based applications. With an in-depth inspection of the electronic structures and bulk lattice symmetries of a variety of systems, we analyze the origin of the spin splitting in two- and three-dimensional hybrid perovskites. It is shown that low-dimensional nanostructures made of CH3NH3PbX3 (X = I, Br) lead to spin splittings that can be controlled by an applied electric field. These findings further open the door for a perovskite-based spintronics. © 2015 American Chemical Society.


  • Tunneling and electronic structure of the two-gap superconductor MgB2

    Silva-Guillén J.A., Noat Y., Cren T., Sacks W., Canadell E., Ordejón P. Physical Review B - Condensed Matter and Materials Physics; 92 (6, 064514) 2015. 10.1103/PhysRevB.92.064514. IF: 3.736

    A combined experimental (superconductor-insulator-superconductor tunneling spectra) and theoretical (density functional theory) study of the two-gap superconductor MgB2 is reported. The calculations confirm that the small gap is associated with a π band mostly based on the boron pz orbitals leading to the three-dimensional band component of the Fermi surface. This channel almost completely dominates the tunneling images and spectra for c-axis-oriented samples and not the two-dimensional σ band. The origin of this effect is due to the faster decay of the electronic states associated with the boron px and py orbitals compared to those associated with the boron pz orbitals, together with the symmetry properties of the wave functions. The calculated tunneling channels and partial density of states for each band agree with the values deduced from precise fits of experimental tunneling spectra. The present approach provides a framework for the understanding of tunneling spectra and the nature of superconducting gaps of other multigap superconductors. © 2015 American Physical Society.


  • Using G0W0 Level Alignment to Identify Catechol's Structure on TiO2(110)

    Mowbray D.J., Migani A. Journal of Physical Chemistry C; 119 (34): 19634 - 19641. 2015. 10.1021/acs.jpcc.5b05392. IF: 4.772

    We perform state-of-the-art calculations for a prototypical dye sensitized solar cell: catechol on rutile TiO2(110). Catechol is often used as an anchoring group for larger more complex organic and inorganic dyes on TiO2 and forms type II heterojunctions on TiO2(110). In particular, we compare quasiparticle (QP) G0W0 with hybrid exchange correlation functional (HSE) density functional theory (DFT) calculations for the catechol-rutile TiO2(110) interface. In so doing, we provide a theoretical interpretation of ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) experiments for this prototypical system. Specifically, we demonstrate that the position, presence, and intensity of peaks associated with catechol's HOMO, intermolecular OH-O bonds, and interfacial hydrogen bonds to the surface bridging O atoms (ObrH-C and ObrH-O) may be used to fingerprint deprotonation of catechol's OH anchoring groups. Furthermore, our results suggest deprotonation of these groups, while being nearly isoenergetic at high coverages, may significantly increase the photovoltaic efficiency of catechol-TiO2(110) interfaces. (Figure Presented). © 2015 American Chemical Society.


2014

  • Classical limit of a quantal nano-magnet in an anisotropic environment

    Gauyacq, J.P.; Lorente, N. Surface Science; 630: 325 - 330. 2014. 10.1016/j.susc.2014.07.013. IF: 1.870


  • Coverage dependence of the level alignment for methanol on TiO2(110)

    Migani, A.; Mowbray, D.J. Computational and Theoretical Chemistry; 1040-1041: 259 - 265. 2014. 10.1016/j.comptc.2014.03.007. IF: 1.368


  • Difficulties in the ab initio description of electron transport through spin filters

    Kepenekian, M.; Gauyacq, J.-P.; Lorente, N. Journal of Physics Condensed Matter; 2014. 10.1088/0953-8984/26/10/104203. IF: 2.223


  • Electron transport signature of H2 dissociation on atomic gold wires

    Zanchet, A.; Roncero, O.; Dorta-Urra, A.; Aguado, A.; Martínez, J.I.; Flores, F.; Lorente, N. Physical Review B; 90 (4) 2014. 10.1103/PhysRevB.90.041404.


  • Electronic properties of single-layer and multilayer transition metal dichalcogenides MX2 (M = Mo, W and X = S, Se)

    Roldán R., Silva-Guillén J.A., López-Sancho M.P., Guinea F., Cappelluti E., Ordejón P. Annalen der Physik; 526 (9-10): 347 - 357. 2014. 10.1002/andp.201400128.

    Single- and few-layer transition metal dichalcogenides have recently emerged as a new family of layered crystals with great interest, not only from the fundamental point of view, but also because of their potential application in ultrathin devices. Here the electronic properties of semiconducting MX2, where M = Mo or W and X = S or Se, are reviewed. Based on of density functional theory calculations, which include the effect of spin-orbit interaction, the band structure of single-layer, bilayer and bulk compounds is discussed. The band structure of these compounds is highly sensitive to elastic deformations, and it is reviewed how strain engineering can be used to manipulate and tune the electronic and optical properties of those materials. Further, the effect of disorder and imperfections in the lattice structure and their effect on the optical and transport properties of MX2 is discussed. The superconducting transition in these compounds, which has been observed experimentally, is analyzed, as well as the different mechanisms proposed so far to explain the pairing. Finally, a discussion on the excitonic effects which are present in these systems is included. © 2014 by Wiley-VCH Verlag GmbH & Co. KGaA.


  • Excitation of bond-alternating spin-1/2 Heisenberg chains by tunnelling electrons

    Gauyacq, J.P.; Lorente, N. Journal of Physics Condensed Matter; 2014. 10.1088/0953-8984/26/39/394005. IF: 2.223


  • Momentum dependence of spin-orbit interaction effects in single-layer and multi-layer transition metal dichalcogenides

    Roldán R., López-Sancho M.P., Guinea F., Cappelluti E., Silva-Guillén J.A., Ordejón P. 2D Materials; 1 (3, 034003) 2014. 10.1088/2053-1583/1/3/034003.

    One of the main characteristics of the new family of two-dimensional crystals of semiconducting transition metal dichalcogenides (TMDs) is the strong spin-orbit interaction, which makes them very promising for future applications in spintronics and valleytronics devices. Here we present a detailed study of the effect of spin-orbit coupling (SOC) on the band structure of single-layer and bulk TMDs, including explicitly the role of the chalcogen orbitals and their hybridization with the transition metal atoms. To this aim, we combine density functional theory (DFT) calculations with a Slater-Koster tight-binding (TB) model. Whereas most of the previous TB models have been restricted to the K and K' points of the Brillouin zone (BZ), here we consider the effect of SOC in the whole BZ, and the results are compared to the band structure obtained by DFT methods. The TB model is used to analyze the effect of SOC in the band structure, considering separately the contributions from the transition metal and the chalcogen atoms. Finally, we present a scenario where, in the case of strong SOC, the spin/orbital/valley entanglement at the minimum of the conduction band at Q can be probed and be of experimental interest in the most common cases of electron-doping reported for this family of compounds. © 2014 IOP Publishing Ltd.


  • Orbital redistribution in molecular nanostructures mediated by metal-organic bonds

    Yang, Z.; Corso, M.; Robles, R.; Lotze, C.; Fitzner, R.; Mena-Osteritz, E.; Bäuerle, P.; Franke, K.J.; Pascual, J.I. ACS Nano; 8 (10): 10715 - 10722. 2014. 10.1021/nn504431e. IF: 12.033


  • Oxygen vacancies in self-assemblies of ceria nanoparticles

    Sk, M.A.; Kozlov, S.M.; Lim, K.H.; Migani, A.; Neyman, K.M. Journal of Materials Chemistry A; 2 (43): 18329 - 18338. 2014. 10.1039/c4ta02200a. IF: 0.000


  • Piezoelectric monolayers as nonlinear energy harvesters

    López-Suárez, M.; Pruneda, M.; Abadal, G.; Rurali, R. Nanotechnology; 2014. 10.1088/0957-4484/25/17/175401. IF: 3.672


  • Quasiparticle level alignment for photocatalytic interfaces

    Migani, A.; Mowbray, D.J.; Zhao, J.; Petek, H.; Rubio, A. Journal of Chemical Theory and Computation; 10 (5): 2103 - 2113. 2014. 10.1021/ct500087v. IF: 5.310


  • Spin transport in dangling-bond wires on doped H-passivated Si(100)

    Kepenekian, M.; Robles, R.; Rurali, R.; Lorente, N. Nanotechnology; 2014. 10.1088/0957-4484/25/46/465703. IF: 3.672


  • Theoretical study on the influence of the Mg2+ and Al3+ octahedral cations on the vibrational spectra of the hydroxy groups of dioctahedral 2:1 phyllosilicate models

    Hernández-Haro, N.; Ortega-Castro, J.,; Pruneda, M.,; Sainz-Díaz, C.I.,; Hernández-Laguna, A. Journal of Molecular Modeling; 20 (9): 2402. 2014. 10.1007/s00894-014-2402-6. IF: 1.867


  • Transport fingerprints at graphene superlattice Dirac points induced by a boron nitride substrate

    Martinez-Gordillo, R.; Roche, S.; Ortmann, F.; Pruneda, M. Physical Review B - Condensed Matter and Materials Physics; 2014. 10.1103/PhysRevB.89.161401. IF: 3.664


2013

  • Adsorption site determination of a molecular monolayer via inelastic tunneling

    Wegner, D.; Yamachika, R.; Zhang, X.; Wang, Y.; Crommie, M.F.; Lorente, N. Nano Letters; 13: 2346 - 2350. 2013. 10.1021/nl304081q. IF: 13.025


  • Controlled manipulation of single atoms and small molecules using the scanning tunnelling microscope

    Morgenstern, K.; Lorente, N.; Rieder, K.-H. Physica Status Solidi (B): Basic Research; 250: 1671 - 1751. 2013. 10.1002/pssb.201248392. IF: 1.489


  • Correlation-mediated processes for electron-induced switching between Néel states of Fe antiferromagnetic chains

    Gauyacq, J.-P.; Yaro, S.M.; Cartoixà, X.; Lorente, N. Physical Review Letters; 110 2013. 10.1103/PhysRevLett.110.087201. IF: 7.943


  • Electron transport through dangling-bond silicon wires on H-passivated Si(100)

    Kepenekian, M.; Novaes, F.D.; Robles, R.; Monturet, S.; Kawai, H.; Joachim, C.; Lorente, N. Journal of Physics Condensed Matter; 25 2013. 10.1088/0953-8984/25/2/025503. IF: 2.355


  • Gold and methane: A noble combination for delicate oxidation

    Mowbray, D.J.; Migani, A.; Walther, G.; Cardamone, D.M.; Rubio, A. Journal of Physical Chemistry Letters; 4: 3006 - 3012. 2013. 10.1021/jz401553p. IF: 6.585


  • Imaging the dynamics of individually adsorbed molecules

    Schaffert, J.; Cottin, M.C.; Sonntag, A.; Karacuban, H.; Bobisch, C.A.; Lorente, N.; Gauyacq, J.-P.; Möller, R. Nature Materials; 12: 223 - 227. 2013. 10.1038/nmat3527. IF: 35.749


  • Impact of vacancies on diffusive and pseudodiffusive electronic transport in graphene

    Cresti, A.; Louvet, T.; Ortmann, F.; Van Tuan, D.; Lenarczyk, P.; Huhs, G.; Roche, S. Crystals; 3 (2): 289 - 305. 2013. 10.3390/cryst3020289. IF: 0.000


  • Leakage current in atomic-size surface interconnects

    Kepenekian, M.; Robles, R.; Joachim, C.; Lorente, N. Applied Physics Letters; 103 2013. 10.1063/1.4825375. IF: 3.794


  • Level alignment of a prototypical photocatalytic system: Methanol on TiO2(110)

    Migani, A.; Mowbray, D.J.; Iacomino, A.; Zhao, J.; Petek, H.; Rubio, A. Journal of the American Chemical Society; 135: 11429 - 11432. 2013. 10.1021/ja4036994. IF: 10.677


  • Magnetic reversal of a quantum nanoferromagnet

    Gauyacq, J.P.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 87 2013. 10.1103/PhysRevB.87.195402. IF: 3.767


  • Manganese 3×3 and √3×√3-R30 â̂̃ structures and structural phase transition on w-GaN(0001̄) studied by scanning tunneling microscopy and first-principles theory

    Chinchore A.V., Wang K., Shi M., Mandru A., Liu Y., Haider M., Smith A.R., Ferrari V., Barral M.A., Ordejón P. Physical Review B - Condensed Matter and Materials Physics; 87 (16, 165426) 2013. 10.1103/PhysRevB.87.165426.

    Manganese deposited on the N-polar face of wurtzite gallium nitride [GaN (0001̄)] results in two unique surface reconstructions, depending on the deposition temperature. At lower temperature (less than 105 â̂̃C), it is found that a metastable 3×3 structure forms. Mild annealing of this Mn 3×3 structure leads to an irreversible phase transition to a different, much more stable √3×√3-R30â̂̃ structure which can withstand high-temperature annealing. Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction data are compared with results from first-principles theoretical calculations. Theory finds a lowest-energy model for the 3×3 structure consisting of Mn trimers bonded to the Ga adlayer atoms but not with N atoms. The lowest-energy model for the more stable √3×√3-R30â̂̃ structure involves Mn atoms substituting for Ga within the Ga adlayer and thus bonding with N atoms. Tersoff-Hamman simulations of the resulting lowest-energy structural models are found to be in very good agreement with the experimental STM images. © 2013 American Physical Society.


  • Modelling the growth of ZnO thin films by PVD methods and the effects of post-annealing

    Blackwell, S.; Smith, R.; Kenny, S.D.; Walls, J.M.; Sanz-Navarro, C.F. Journal of Physics Condensed Matter; 25 2013. 10.1088/0953-8984/25/13/135002. IF: 2.355


  • Nitrogen-doped graphitic nanoribbons: Synthesis, characterization, and transport

    Ortiz-Medina, J.; García-Betancourt, M.L.; Jia, X.; Martínez-Gordillo, R.; Pelagio-Flores, M.A.; Swanson, D.; Elías, A.L.; Gutiérrez, H.R.; Gracia-Espino, E.; Meunier, V.; Owens, J.; Sumpter, B.G.; Cruz-Silva, E.; Rodríguez-Macías, F.J.; Lõpez-Urías, F.; Muñoz-Sandoval, E.; Dresselhaus, M.S.; Terrones, H.; Terrones, M. Advanced Functional Materials; 23: 3755 - 3762. 2013. 10.1002/adfm.201202947. IF: 9.765


  • Site- and orbital-dependent charge donation and spin manipulation in electron-doped metal phthalocyanines

    Krull, C.; Robles, R.; Mugarza, A.; Gambardella, P. Nature Materials; 12: 337 - 343. 2013. 10.1038/nmat3547. IF: 35.749


  • Surface-induced dechlorination of FeOEP-Cl** on Cu(111)

    Van Vörden, D.; Lange, M.; Schaffert, J.; Cottin, M.C.; Schmuck, M.; Robles, R.; Wende, H.; Bobisch, C.A.; Möller, R. Chemphyschem : a European journal of chemical physics and physical chemistry; 14: 3472 - 3475. 2013. 10.1002/cphc.201300497. IF: 3.349


  • Surface-state engineering for interconnects on H-passivated Si(100)

    Kepenekian, M.; Robles, R.; Joachim, C.; Lorente, N. Nano Letters; 13: 1192 - 1195. 2013. 10.1021/nl304611m. IF: 13.025


  • Surface-supported supramolecular pentamers

    Karan, S.; Wang, Y.; Robles, R.; Lorente, N.; Berndt, R. Journal of the American Chemical Society; 135: 14004 - 14007. 2013. 10.1021/ja405456k. IF: 10.677


  • Tight-binding model and direct-gap/indirect-gap transition in single-layer and multilayer MoS2

    Cappelluti E., Roldán R., Silva-Guillén J.A., Ordejón P., Guinea F. Physical Review B - Condensed Matter and Materials Physics; 88 (7, 075409) 2013. 10.1103/PhysRevB.88.075409.

    In this paper we present a paradigmatic tight-binding model for single-layer as well as multilayered semiconducting MoS2 and similar transition metal dichalcogenides. We show that the electronic properties of multilayer systems can be reproduced in terms of a tight-binding modeling of the single-layer hopping terms by simply adding the proper interlayer hoppings ruled by the chalcogenide atoms. We show that such a tight-binding model makes it possible to understand and control in a natural way the transition between a direct-gap band structure, in single-layer systems, and an indirect gap in multilayer compounds in terms of a momentum/orbital selective interlayer splitting of the relevant valence and conduction bands. The model represents also a suitable playground to investigate in an analytical way strain and finite-size effects. © 2013 American Physical Society.


  • Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111)

    Schaffert, J.; Cottin, M.C.; Sonntag, A.; Bobisch, C.A.; Möller, R.; Gauyacq, J.-P.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 88 2013. 10.1103/PhysRevB.88.075410. IF: 3.767


  • Vibrational transition rule during a through-bond electron transfer process

    Monturet, S.; Kepenekian, M.; Robles, R.; Lorente, N.; Joachim, C. Chemical Physics Letters; 567: 1 - 5. 2013. 10.1016/j.cplett.2013.02.057. IF: 2.145


2012

  • A theoretical rationalization of a total inelastic electron tunneling spectrum: The comparative cases of formate and benzoate on Cu(111)

    Burema, S.R.; Lorente, N.; Bocquet, M.-L. Journal of Chemical Physics; 136 2012. 10.1063/1.4730168.


  • Calculation of core level shifts within DFT using pseudopotentials and localized basis sets

    García-Gil S., García A., Ordejón P. European Physical Journal B; 85 (7, 239) 2012. 10.1140/epjb/e2012-30334-5.

    The calculation of core level shifts can be done in the context of density functional theory (DFT) using different approaches and physical approximations to the photoemission process. The initial state and the SCF approximations are the most commonly used ones. Here, we describe the details of their implementation in the context of DFT using pseudopotentials and localized atomic orbitals as a basis set, and in particular as applied to the Siesta code. We give a full account of the technicalities involved in these calculations, including the details of the ionic pseudopotential generation, basis sets, charge states and reference potential. We test the method by computing the core level shifts of the Si 2p level for a series of molecules and the p(2×2) asymmetric-dimer reconstruction of the Si(001) surface. © EDP Sciences, Societá Italiana di Fisica, Springer-Verlag 2012.


  • Carbon nanotubes as substrates for molecular spiropyran-based switches

    Malic, E.; Setaro, A.; Bluemmel, P.; Sanz-Navarro, C.F.; Ordejón, P.; Reich, S.; Knorr, A. Journal of Physics Condensed Matter; 24: 394006. 2012. .


  • Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets

    Hübener H., Pérez-Osorio M.A., Ordejón P., Giustino F. Physical Review B - Condensed Matter and Materials Physics; 85 (24, 245125) 2012. 10.1103/PhysRevB.85.245125.

    We develop a first-principles computational method for investigating the dielectric screening in extended systems using the self-consistent Sternheimer equation and localized nonorthogonal basis sets. Our approach does not require the explicit calculation of unoccupied electronic states, uses only two-center integrals, and has a theoretical scaling of order O(N3). We demonstrate this method by comparing our calculations for silicon, germanium, diamond, and LiCl with reference plane-wave calculations. We show that accuracy comparable to that of plane-wave calculations can be achieved via a systematic optimization of the basis set. © 2012 American Physical Society.


  • Electrochemical ferroelectric switching: Origin of polarization reversal in ultrathin films

    Bristowe, N.C.; Stengel, M.; Littlewood, P.B.; Pruneda, J.M.; Artacho, E. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.024106.


  • Electronic and magnetic properties of molecule-metal interfaces: Transition-metal phthalocyanines adsorbed on Ag(100)

    Mugarza, A.; Robles, R.; Krull, C.; Korytár, R.; Lorente, N.; Gambardella, P. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.155437.


  • Electroresistance effect in ferroelectric tunnel junctions with symmetric electrodes

    Bilc D.I., Novaes F.D., Íñiguez J., Ordejón P., Ghosez P. ACS Nano; 6 (2): 1473 - 1478. 2012. 10.1021/nn2043324.

    Understanding the effects that govern electronic transport in ferroelectric tunnel junctions (FTJs) is of vital importance to improve the efficiency of devices such as ferroelectric memories with nondestructive readout. However, our current knowledge (typically based on simple semiempirical models or first-principles calculations restricted to the limit of zero bias) remains partial, which may hinder the development of more efficient systems. For example, nowadays it is commonly believed that the tunnel electroresistance (TER) effect exploited in such devices mandatorily requires, to be sizable, the use of two different electrodes, with related potential drawbacks concerning retention time, switching, and polarization imprint. In contrast, here we demonstrate at the first-principles level that large TER values of about 200% can be achieved under finite bias in a prototypical FTJ with symmetric electrodes. Our atomistic approach allows us to quantify the contribution of different microscopic mechanisms to the electroresistance, revealing the dominant role of the inverse piezoelectric response of the ferroelectric. On the basis of our analysis, we provide a critical discussion of the semiempirical models traditionally used to describe FTJs. © 2012 American Chemical Society.


  • Energetics and stability of dangling-bond silicon wires on H passivated Si(100)

    Robles, R.; Kepenekian, M.; Monturet, S.; Joachim, C.; Lorente, N. Journal of Physics Condensed Matter; 24 2012. 10.1088/0953-8984/24/44/445004.


  • Excitation of local magnetic moments by tunneling electrons

    Gauyacq, J.-P.; Lorente, N.; Novaes, F.D. Progress in Surface Science; 87: 63 - 107. 2012. 10.1016/j.progsurf.2012.05.003.


  • Insulating behavior of an amorphous graphene membrane

    Van Tuan D., Kumar A., Roche S., Ortmann F., Thorpe M.F., Ordejon P. Physical Review B - Condensed Matter and Materials Physics; 86 (12, 121408) 2012. 10.1103/PhysRevB.86.121408.

    We investigate the charge transport properties of planar amorphous graphene that is fully topologically disordered, in the form of sp2 threefold coordinated networks consisting of hexagonal rings but also including many pentagons and heptagons distributed in a random fashion. Using the Kubo transport methodology and the Lanczos method, the density of states, mean free paths, and semiclassical conductivities of such amorphous graphene membranes are computed. Despite a large increase in the density of states close to the charge neutrality point, all electronic properties are dramatically degraded, evidencing an Anderson insulating state caused by topological disorder alone. These results are supported by Landauer-Büttiker conductance calculations, which show a localization length as short as 5 nm. © 2012 American Physical Society.


  • Lifetime of magnetic excitations in supported ferromagnetic and antiferromagnetic spin-12 Heisenberg chains

    Gauyacq, J.P.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.115420.


  • Many-body effects in magnetic inelastic electron tunneling spectroscopy

    Korytár, R.; Lorente, N.; Gauyacq, J.-P. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.125434.


  • Native defects in hybrid C/BN nanostructures by density functional theory calculations

    Pruneda, J.M. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.045422.


  • Performance of local orbital basis sets in the self-consistent Sternheimer method for dielectric matrices of extended systems

    Hubene, H.; Perez-Osorio, M.A.; Ordejon, P.; Giustino, F. European Physical Journal B; 85: 321. 2012. .


  • Spin doping of individual molecules by using single-atom manipulation

    Robles, R.; Lorente, N.; Isshiki, H.; Liu, J.; Katoh, K.; Breedlove, B.K.; Yamashita, M.; Komeda, T. Nano Letters; 12: 3609 - 3612. 2012. 10.1021/nl301301e.


  • Y:BaZrO 3 perovskite compounds I: DFT study on the unprotonated and protonated local structures

    Cammarata A., Ordejón P., Emanuele A., Duca D. Chemistry - An Asian Journal; 7 (8): 1827 - 1837. 2012. 10.1002/asia.201100974.

    Y-doped BaZrO 3 derivatives were studied by density functional theory (DFT) to investigate the local arrangements of the octahedral sites in Pm${\bar 3}$m cubic frameworks. Single- and double substitution of zirconium by yttrium were considered, including in the presence of a nearby oxygen vacancy. Although the structural symmetry of undoped barium zirconate was not modified after yttrium doping, the presence of yttrium induced several differences in the oxygen sites around it, according to the local geometrical arrangement of yttrium in the host matrix. As an example, the differences between such oxygen sites were shown in the presence of a proton. In this case, different stabilization energies characterized the protonated fragments. Only in those structures, in which two yttrium atoms were neighbors (i.e., formed Y-O-Y moieties), were the relative energy differences between the corresponding proton stable sites in agreement with the order of magnitude of the experimental proton-hopping activation energies. The distribution of such energy differences suggested a grouping of the oxygen atoms into three sets, which had peculiar structural features that weren't easily deducible from their topologies. The existence of proton traps was also discussed on the basis of the energy-difference distributions. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


2011

  • An efficient implementation of a QM-MM method in SIESTA

    Sanz-Navarro C.F., Grima R., García A., Bea E.A., Soba A., Cela J.M., Ordejón P. Theoretical Chemistry Accounts; 128 (4): 825 - 833. 2011. 10.1007/s00214-010-0816-5.

    We present the major features of a new implementation of a QM-MM method that uses the DFT code Siesta to treat the quantum mechanical subsystem and the AMBER force field to deal with the classical part. The computation of the electrostatic interaction has been completely revamped to treat periodic boundary conditions exactly, using a real-space grid that encompasses the whole system. Additionally, we present a new parallelization of the Siesta grid operations that provides near-perfect load balancing for all the relevant operations and achieves a much better scalability, which is important for efficient massive QM-MM calculations in which the grid can potentially be very large. © 2010 Springer-Verlag.


  • Cis-dicarbonyl binding at cobalt and iron porphyrins with saddle-shape conformation

    Seufert, K.; Bocquet, M.-L.; Auwärter, W.; Weber-Bargioni, A.; Reichert, J.; Lorente, N.; Barth, J.V. Nature Chemistry; 3: 114 - 119. 2011. 10.1038/nchem.956.


  • Excitation of spin waves by tunneling electrons in ferromagnetic and antiferromagnetic spin-12 Heisenberg chains

    Gauyacq, J.P.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 83 2011. 10.1103/PhysRevB.83.035418.


  • Magnetic excitation by tunneling electrons of frustrated ferromagnetic spin-12 chains and rings

    Gauyacq, J.P.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 84 2011. 10.1103/PhysRevB.84.085415.


  • Magnetism-dependent transport phenomena in hydrogenated graphene: From spin-splitting to localization effects

    Leconte N., Soriano D., Roche S., Ordejon P., Charlier J.-C., Palacios J.J. ACS Nano; 5 (5): 3987 - 3992. 2011. 10.1021/nn200558d.

    Spin-dependent transport in hydrogenated two-dimensional graphene is explored theoretically. Adsorbed atomic hydrogen impurities can either induce a local antiferromagnetic, ferromagnetic, or nonmagnetic state depending on their density and relative distribution. To describe the various magnetic possibilities of hydrogenated graphene, a self-consistent Hubbard Hamiltonian, optimized by ab initio calculations, is first solved in the mean field approximation for small graphene cells. Then, an efficient order N Kubo transport methodology is implemented, enabling large scale simulations of functionalized graphene. Depending on the underlying intrinsic magnetic ordering of hydrogen-induced spins, remarkably different transport features are predicted for the same impurity concentration. Indeed, while the disordered nonmagnetic graphene system exhibits a transition from diffusive to localization regimes, the intrinsic ferromagnetic state exhibits unprecedented robustness toward quantum interference, maintaining, for certain resonant energies, a quasiballistic regime up to the micrometer scale. Consequently, low temperature transport measurements could unveil the presence of a magnetic state in weakly hydrogenated graphene. © 2011 American Chemical Society.


  • Magnetoresistance and magnetic ordering fingerprints in hydrogenated graphene

    Soriano D., Leconte N., Ordejón P., Charlier J.-C., Palacios J.-J., Roche S. Physical Review Letters; 107 (1, 016602) 2011. 10.1103/PhysRevLett.107.016602.

    Spin-dependent features in the conductivity of graphene, chemically modified by a random distribution of hydrogen adatoms, are explored theoretically. The spin effects are taken into account using a mean-field self-consistent Hubbard model derived from first-principles calculations. A Kubo transport methodology is used to compute the spin-dependent transport fingerprints of weakly hydrogenated graphene-based systems with realistic sizes. Conductivity responses are obtained for paramagnetic, antiferromagnetic, or ferromagnetic macroscopic states, constructed from the mean-field solutions obtained for small graphene supercells. Magnetoresistance signals up to ∼7% are calculated for hydrogen densities around 0.25%. These theoretical results could serve as guidance for experimental observation of induced magnetism in graphene. © 2011 American Physical Society.


  • Modulation of surface charge transfer through competing long-range repulsive versus short-range attractive interactions

    Fraxedas J., García-Gil S., Monturet S., Lorente N., Fernández-Torrente I., Franke K.J., Pascual J.I., Vollmer A., Blum R.-P., Koch N., Ordejón P. Journal of Physical Chemistry C; 115 (38): 18640 - 18648. 2011. 10.1021/jp2050838.

    We report a combined experimental and theoretical study of the modulation of surface charge transfer on the tetrathiafulvalene (TTF)/Au(111) interface as a function of coverage in the submonolayer regime by combining low-temperature scanning tunneling microscopy, high-resolution photoemission spectroscopy using synchrotron radiation, and density functional theory (DFT) calculations. The modulation is induced by the competition between long-range repulsive Coulombic interactions and short-range attractive hydrogen-bonding interactions. The system shows the characteristic pattern evolution, from monomeric stripes at low coverages to two-dimensional islands, with the formation of labyrinths in the crossover. © 2011 American Chemical Society.


  • Multi-orbital non-crossing approximation from maximally localized Wannier functions: The Kondo signature of copper phthalocyanine on Ag(100)

    Korytr, R.; Lorente, N. Journal of Physics Condensed Matter; 23 2011. 10.1088/0953-8984/23/35/355009.


  • Observation and electric current control of a local spin in a single-molecule magnet

    Komeda, T.; Isshiki, H.; Liu, J.; Zhang, Y.F.; Lorente, N.; Katoh, K.; Breedlove, B.K.; Yamashita, M. Nature Communications; 2 2011. 10.1038/ncomms1210.


  • Oxygen surface functionalization of graphene nanoribbons for transport gap engineering

    Cresti A., Lopez-Bezanilla A., Ordejón P., Roche S. ACS Nano; 5 (11): 9271 - 9277. 2011. 10.1021/nn203573y.

    We numerically investigate the impact of epoxide adsorbates on the transport properties of graphene nanoribbons with width varying from a few nanometers to 15 nm. For the wider ribbons, a scaling analysis of conductance properties is performed for adsorbate density ranging from 0.1% to 0.5%. Oxygen atoms introduce a large electron-hole transport asymmetry with mean free paths changing by up to 1 order of magnitude, depending on the hole or electron nature of charge carriers. The opening of a transport gap on the electron side for GNRs as wide as 15 nm could be further exploited to control current flow and achieve larger ON/OFF ratios, despite the initially small intrinsic energy gap. The effect of the adsorbates in narrow ribbons is also investigated by full ab initio calculations to explore the limit of ultimate downsized systems. In this case, the inhomogeneous distribution of adsorbates and their interplay with the ribbon edge are found to play an important role. © 2011 American Chemical Society.


  • Quantum transport in chemically modified two-dimensional graphene: From minimal conductivity to Anderson localization

    Leconte N., Lherbier A., Varchon F., Ordejon P., Roche S., Charlier J.-C. Physical Review B - Condensed Matter and Materials Physics; 84 (23, 235420) 2011. 10.1103/PhysRevB.84.235420.

    An efficient computational methodology is used to explore charge transport properties in chemically modified (and randomly disordered) graphene-based materials. The Hamiltonians of various complex forms of graphene are constructed using tight-binding models enriched by first-principles calculations. These atomistic models are further implemented into a real-space order-N Kubo-Greenwood approach, giving access to the main transport length scales (mean free paths, localization lengths) as a function of defect density and charge carrier energy. An extensive investigation is performed for epoxide impurities with specific discussions on both the existence of a minimum semiclassical conductivity and a crossover between weak to strong localization regime. The 2D generalization of the Thouless relationship linking transport length scales is here illustrated based on a realistic disorder model. © 2011 American Physical Society.


  • Spin coupling and relaxation inside molecule-metal contacts.

    Mugarza, A.; Krull, C.; Robles, R.; Stepanow, S.; Ceballos, G.; Gambardella, P. Nature Communications; 2 2011. 10.1038/ncomms1497.


  • Structural, dynamical, and electronic transport properties of modified DNA duplexes containing size-expanded nucleobases

    Blas J.R., Huertas O., Tabares C., Sumpter B.G., Fuentes-Cabrera M., Orozco M., Ordejón P., Luque F.J. Journal of Physical Chemistry A; 115 (41): 11344 - 11354. 2011. 10.1021/jp205122c.

    Among the distinct strategies proposed to expand the genetic alphabet, size-expanded nucleobases are promising for the development of modified DNA duplexes with improved biotechnological properties. In particular, duplexes built up by replacing canonical bases with the corresponding benzo-fused counterparts could be valuable as molecular nanowires. In this context, this study reports the results of classical molecular dynamics simulations carried out to examine the structural and dynamical features of size-expanded DNAs, including both hybrid duplexes containing mixed pairs of natural and benzo-fused bases (xDNA) and pure size-expanded (xxDNA) duplexes. Furthermore, the electronic structure of both natural and size-expanded duplexes is examined by means of density functional computations. The results confirm that the structural and flexibility properties of the canonical DNA are globally little affected by the presence of benzo-fused bases. The most relevant differences are found in the enhanced size of the grooves, and the reduction in the twist. However, the analysis also reveals subtle structural effects related to the nature and sequence of benzo-fused bases in the duplex. On the other hand, electronic structure calculations performed for xxDNAs confirm the reduction in the HOMO-LUMO gap predicted from the analysis of the natural bases and their size-expanded counterparts, which suggests that pure size-expanded DNAs can be good conductors. A more complex situation is found for xDNAs, where fluctuations in the electrostatic interaction between base pairs exerts a decisive influence on the modulation of the energy gap. © 2011 American Chemical Society.


  • Theoretical study of magnetic moments induced by defects at the SiC(110) surface

    Poissier, A.; Lorente, N.; Yndurain, F. Physical Review B - Condensed Matter and Materials Physics; 83 2011. 10.1103/PhysRevB.83.035322.


2010

  • Band selection and disentanglement using maximally localized Wannier functions: The cases of Co impurities in bulk copper and the Cu(111) surface

    Korytár R., Pruneda M., Junquera J., Ordejón P., Lorente N. Journal of Physics Condensed Matter; 22 (38, 385601) 2010. 10.1088/0953-8984/22/38/385601.

    We have adapted the maximally localized Wannier function approach of Souza et al (2002 Phys. Rev. B 65 035109) to the density functional theory based Siesta code (Soler et al 2002 J. Phys.: Condens. Mater. 14 2745) and applied it to the study of Co substitutional impurities in bulk copper as well as to the Cu(111) surface. In the Co impurity case, we have reduced the problem to the Co d-electrons and the Cu sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined density functional parameters in a fully orthonormal basis set. In order to test the quality of the Wannier approach to surfaces, we have studied the electronic structure of the Cu(111) surface by again transforming the density functional problem into the Wannier representation. An excellent description of the Shockley surface state is attained, permitting us to be confident in the application of this method to future studies of magnetic adsorbates in the presence of an extended surface state. © 2010 IOP Publishing Ltd.


  • Damaging graphene with ozone treatment: A chemically tunable metal - Insulator transition

    Leconte N., Moser J., Ordejón P., Tao H., Lherbier A., Bachtold A., Alsina F., Sotomayor Torres C.M., Charlier J.-C., Roche S. ACS Nano; 4 (7): 4033 - 4038. 2010. 10.1021/nn100537z.

    We present a multiscale ab initio study of electronic and transport properties of two-dimensional graphene after epoxide functionalization via ozone treatment. The orbital rehybridization induced by the epoxide groups triggers a strong intervalley scattering and changes dramatically the conduction properties of graphene. By varying the coverage density of epoxide defects from 0.1 to 4%, charge conduction can be tuned from a diffusive to a strongly localized regime, with localization lengths down to a few nanometers long. Experimental results supporting the interpretation as a metal - insulator transition are also provided. © 2010 American Chemical Society.


  • Density-wave instability in α- ( BEDT-TTF)2KHg(SCN) 4 studied by x-ray diffuse scattering and by first-principles calculations

    Foury-Leylekian P., Pouget J.-P., Lee Y.-J., Nieminen R.M., Ordejón P., Canadell E. Physical Review B - Condensed Matter and Materials Physics; 82 (13, 134116) 2010. 10.1103/PhysRevB.82.134116.

    α- (BEDT-TTF)2KHg(SCN)4 develops a density wave ground state below 8 K whose origin is still debated. Here we report a combined x-ray diffuse scattering and first-principles density functional theory study supporting the charge density wave (CDW) scenario. In particular, we observe a triply incommensurate anharmonic lattice modulation with intralayer wave vector components which coincide within experimental errors to the maximum of the calculated Lindhard response function. A detailed study of the structural aspects of the modulation shows that the CDW instability in α- ( BEDT-TTF) 2 KHg ( SCN) 4 is considerably more involved than those following a standard Peierls mechanism. We thus propose a microscopic mechanism where the CDW instability of the BEDT-TTF layer is triggered by the anion sublattice. Our mechanism also emphasizes the key role of the coupling of the BEDT-TTF and anion layers via the hydrogen bond network to set the global modulation. © 2010 The American Physical Society.


  • Electronic transport between graphene layers covalently connected by carbon nanotubes

    Novaes F.D., Rurali R., Ordejón P. ACS Nano; 4 (12): 7596 - 7602. 2010. 10.1021/nn102206n.

    We present a first-principles study of the electronic transport properties of metallic and semiconducting carbon nanotube (CNT) junctions connecting two graphene layers, for different CNT lengths and link structures. Transport is analyzed in terms of the scattering states originated from the π and π* states of the finite-length CNTs, which couple to the graphene states producing resonances in the transmission curves. We find that, for metallic CNTs, the conductance is nearly independent of the tube length, but changes strongly with the link structure, while the opposite occurs for semiconducting CNTs, where the conductance in the tunneling regime is mainly controlled by the tube length and independent of the link structure. The sizable band offset between graphene and the CNTs yields to considerable effects on the transport properties, which cannot be captured using simple empirical models and highlights the need for a first-principles description. © 2010 American Chemical Society.


  • Graphene on Ru(0001): Contact formation and chemical reactivity on the atomic scale

    Altenburg, S.J.; Kröger, J.; Wang, B.; Bocquet, M.L.; Lorente, N.; Berndt, R. Physical Review Letters; 105 2010. 10.1103/PhysRevLett.105.236101.


  • Growth and Structure of Self-assembled Monolayers of a TTF Derivative on Au(111)

    Urban, C.; Écija, D.; Wang, Y.; Trelka, M.; Preda, I.; Vollmer, A.; Lorente, N.; Arnau, A.; Alcamí, M.; Soriano, L.; Martín, N.; Martín, F.; Otero, R.; Gallego, J.M.; Miranda, R. Journal of Physical Chemistry C; 114: 6503 - 6510. 2010. 10.1021/jp911839b.


  • Magnetic transitions induced by tunneling electrons in individual adsorbed M -phthalocyanine molecules (M=Fe and Co)

    Gauyacq, J.-P.; Novaes, F.D.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 81 2010. 10.1103/PhysRevB.81.165423.


  • Mixed-valency signature in vibrational inelastic electron tunneling spectroscopy

    Alducin, M.; Sánchez-Portal, D.; Arnau, A.; Lorente, N. Physical Review Letters; 104 2010. 10.1103/PhysRevLett.104.136101.


  • Orbital specific chirality and homochiral self-assembly of achiral molecules induced by charge transfer and spontaneous symmetry breaking

    Mugarza A., Lorente N., Ordejón P., Krull C., Stepanow S., Bocquet M.-L., Fraxedas J., Ceballos G., Gambardella P. Physical Review Letters; 105 (11, 115702) 2010. 10.1103/PhysRevLett.105.115702.

    We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers. © 2010 The American Physical Society.


  • Origin of half-semimetallicity induced at interfaces of C-BN heterostructures

    Pruneda, J.M. Physical Review B - Condensed Matter and Materials Physics; 81 2010. 10.1103/PhysRevB.81.161409.


  • Preface: Phys. stat. sol. (c) 7/11-12

    Correia, A.; Sáenz, J.J.; Ordejon, P.; Roche, S. Physica Status Solidi (C) Current Topics in Solid State Physics; 7: 2593 - 2595. 2010. 10.1002/pssc.201060100.


  • Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100)

    Novaes, F.D.; Lorente, N.; Gauyacq, J.-P. Physical Review B - Condensed Matter and Materials Physics; 82 2010. 10.1103/PhysRevB.82.155401.


  • Real-time TD-DFT simulations in dye sensitized solar cells: The electronic absorption spectrum of alizarin supported on TiO2 nanoclusters

    Sánchez-De-Armas R., Oviedo López J., San-Miguel M.A., Sanz J.F., Ordejón P., Pruneda M. Journal of Chemical Theory and Computation; 6 (9): 2856 - 2865. 2010. 10.1021/ct100289t.

    The structural and electronic properties of the alizarin dye supported on TiO2 nanoclusters have been examined by means of time-dependent density-functional (TD-DFT) calculations performed in the time-domain framework. The calculated electronic absorption spectrum of free alizarin shows a first band centered at 2.67 eV that upon adsorption features a red shift by 0.31 eV, in agreement with both experimental and previous theoretical work. This red shift arises from a relative stabilization of the dye LUMO when adsorbed. To analyze the dependence of the electronic properties of the dye-support couple on the size of metal-oxide nanoparticles, different models of (TiO 2)n nanoclusters have been used (with n = 1, 2, 3, 6, 9, 15, and 38). As a conclusion, the minimal model is good enough to theoretically reproduce the main feature in the spectrum (i.e., the energy shift of the main band upon binding to TiO2). However, it fails in creating intermediate states which could play a significant role under real experimental conditions (dynamics of the electronic transfer). Indeed, as the size of the nanocluster grows, the dye LUMO moves from the edge to well inside the conduction band (Ti 3d band). On the other hand, to assess the consistency of the time-domain approach in the case of such systems, conventional (frequency-domain) TD-DFT calculations have been carried out. It is found that, as far as the functional and basis set are equivalent, both approaches lead to similar results. While for small systems the standard TD-DFT is better suited, for medium to large sized systems, the real-time TD-DFT becomes competitive and more efficient. © 2010 American Chemical Society.


  • Role of molecular electronic structure in inelastic electron tunneling spectroscopy: O2 on Ag(110)

    Monturet, S.; Alducin, M.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 82 2010. 10.1103/PhysRevB.82.085447.


2009

  • Efficient spin transitions in inelastic electron tunneling spectroscopy

    Lorente, N.; Gauyacq, J.-P. Physical Review Letters; 103 2009. 10.1103/PhysRevLett.103.176601.


  • He-LiF surface interaction potential from fast atom diffraction

    Schüller, A.; Winter, H.; Gravielle, M.S.; Pruneda, J.M.; Miraglia, J.E. PHYSICAL REVIEW A; 80 2009. 10.1103/PhysRevA.80.062903.


  • Nonadiabatic wavepacket dynamics: K-space formulation

    Pruneda, J.M.; Souza, I. Physical Review B - Condensed Matter and Materials Physics; 79 2009. 10.1103/PhysRevB.79.045127.


  • Optimal strictly localized basis sets for noble metal surfaces

    García-Gil S., García A., Lorente N., Ordejón P. Physical Review B - Condensed Matter and Materials Physics; 79 (7, 075441) 2009. 10.1103/PhysRevB.79.075441.

    The properties of the (111) surfaces of Cu, Ag, and Au are evaluated using a first-principles approach with strictly localized basis sets. These surfaces present metallic and extended properties that are a priori difficult to describe with a local-basis approach. We explore methodologies to enhance the basis sets of the surface atoms in order to accurately describe surface properties such as surface energies, surface states, and work functions. In this way, the advantages of local-basis computations (namely, efficiency, optimum size scaling, and a natural description of bonding in real space) can be retained, while keeping the accuracy in the description of the properties of the surface at a very good level. © 2009 The American Physical Society.


  • Physica Status Solidi C: Preface

    Correia, A.; Sáenz, J.J.; Ordejón, P. Physica Status Solidi (C) Current Topics in Solid State Physics; 6: 2093 - 2095. 2009. 10.1002/pssc.200960073.


  • Probing the proton location in a water bilayer on Pd (111) by inelastic spectroscopy simulations

    Bocquet, M.-L.; Lorente, N. Journal of Chemical Physics; 130 2009. 10.1063/1.3089824.


  • Selective scanning tunnelling microscope electron-induced reactions of single biphenyl molecules on a Si(100) surface

    Riedel, D.; Bocquet, M.-L.; Lesnard, H.; Lastapis, M.; Lorente, N.; Sonnet, P.; Dujardin, G. Journal of the American Chemical Society; 131: 7344 - 7352. 2009. 10.1021/ja8101133.


  • Solid-state physics: Lost magnetic moments

    Korytár, R.; Lorente, N. Nature; 458: 1123 - 1124. 2009. 10.1038/4581123a.


  • Tunneling spectroscopy in core/shell structured Fe/MgO nanospheres

    Martínez-Boubeta C., Balcells Li., Monty C., Ordejon P., Martínez B. Applied Physics Letters; 94 (6, 062507) 2009. 10.1063/1.3080657.

    We report on tunneling conductance properties of a single Fe island enclosed by an epitaxial MgO shell. The results obtained show clear oscillations in the current-voltage curves that, along with the theoretical modeling, allow determining the electronic density of states of the iron core. Moreover, the correlation of these results with the temperature dependence of the electrical conductivity of assemblies of Fe/MgO nanocrystals provides evidence of the Δ1 symmetry-sensitive tunneling across a crystalline magnesia barrier. © 2009 American Institute of Physics.


2008

  • Adsorption of N2O on Cu(100): A combined scanning tunneling microscopy and density functional theory study

    Franke, K.J.; Fernández-Torrente, I.; Pascual, J.I.; Lorente, N. Physical Chemistry Chemical Physics; 10: 1640 - 1647. 2008. 10.1039/b716952c.


  • Band bending and quasi-2deg in the metallized β-SiC(001) surface

    Rurali R., Wachowicz E., Hyldgaard P., Ordejón P. Physica Status Solidi - Rapid Research Letters; 2 (5): 218 - 220. 2008. 10.1002/pssr.200802166.

    We study the mechanism leading to the metallization of the β-SiC(001) Si-rich surface induced by hydrogen adsorption. We analyze the effects of band bending and demonstrate the existence of a quasi-2D electron gas, which originates from the donation of electrons from adsorbed hydrogen to bulk conduction states. We also provide a simple model that captures the main features of the results of first-principles calculations, and uncovers the basic physics of the process. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


  • Creating pseudo-Kondo resonances by field-induced diffusion of atomic hydrogen

    Hofer, W.A.; Teobaldi, G.; Lorente, N. Nanotechnology; 19 2008. 10.1088/0957-4484/19/30/305701.


  • Dynamic Jahn-Teller effect in electronic transport through single C 60 molecules

    Frederiksen, T.; Franke, K.J.; Arnau, A.; Schulze, G.; Pascual, J.I.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 78 2008. 10.1103/PhysRevB.78.233401.


  • Formation of dispersive hybrid bands at an organic-metal interface

    Gonzalez-Lakunza, N.; Fernández-Torrente, I.; Franke, K.J.; Lorente, N.; Arnau, A.; Pascual, J.I. Physical Review Letters; 100 2008. 10.1103/PhysRevLett.100.156805.


  • Inelastic effects in electron transport studied with wave packet propagation

    Monturet, S.; Lorente, N. Physical Review B - Condensed Matter and Materials Physics; 78 2008. 10.1103/PhysRevB.78.035445.


  • Reducing the molecule-substrate coupling in C60-based nanostructures by molecular interactions

    Franke, K.J.; Schulze, G.; Henningsen, N.; Fernández-Torrente, I.; Pascual, J.I.; Zarwell, S.; Rück-Braun, K.; Cobian, M.; Lorente, N. Physical Review Letters; 100 2008. 10.1103/PhysRevLett.100.036807.


  • The SIESTA method; Developments and applicability

    Artacho E., Anglada E., Diéguez O., Gale J.D., García A., Junquera J., Martin R.M., Ordejón P., Pruneda J.M., Sánchez-Portal D., Soler J.M. Journal of Physics Condensed Matter; 20 (6, 064208) 2008. 10.1088/0953-8984/20/6/064208.

    Recent developments in and around the SIESTA method of first-principles simulation of condensed matter are described and reviewed, with emphasis on (i) the applicability of the method for large and varied systems, (ii) efficient basis sets for the standards of accuracy of density-functional methods, (iii) new implementations, and (iv) extensions beyond ground-state calculations. © 2008 IOP Publishing Ltd.


  • Theoretical study of benzene and pyridine STM-induced reactions on copper surfaces

    Lesnard, H.; Lorente, N.; Bocquet, M.-L. Journal of Physics Condensed Matter; 20 2008. 10.1088/0953-8984/20/22/224012.


  • Unified description of inelastic propensity rules for electron transport through nanoscale junctions

    Paulsson, M.; Frederiksen, T.; Ueba, H.; Lorente, N.; Brandbyge, M. Physical Review Letters; 100 2008. 10.1103/PhysRevLett.100.226604.


2007

  • Chemisorption of sulfur and sulfur-based simple molecules on Au(111)

    Gonzalez-Lakunza, N.; Lorente, N.; Arnau, A. Journal of Physical Chemistry C; 111: 12383 - 12390. 2007. 10.1021/jp0726586.


  • GaS and InSe equations of state from single crystal diffraction

    J. Pellicer-Porres; E. Machado-Charry; A. Segura; S. Gilliland; E. Canadell; P. Ordejón; A. Polian; P. Munsch; A. Chevy y N. Guignot Physica Status Solidi (B): Basic Research; 2007. .


  • Including the probe tip in theoretical models of inelastic scanning tunneling spectroscopy: CO on Cu(100)

    Teobaldi, G.; Peñalba, M.; Arnau, A.; Lorente, N.; Hofer, W.A. Physical Review B - Condensed Matter and Materials Physics; 76 2007. 10.1103/PhysRevB.76.235407.


  • Interaction of copper organometallic precursors with barrier layers of Ti, Ta and W and their nitrides: a first-principles molecular dynamics study

    E. Machado; M. Kaczmarski; B. Braida; P. Ordejón; D. Garg; J. Norman; H. Cheng Journal of Molecular Modeling; 2007. .


  • Long-range repulsive interaction between molecules on a metal surface induced by charge transfer

    Fernandez-Torrente, I.; Monturet, S.; Franke, K.J.; Fraxedas, J.; Lorente, N.; Pascual, J.I. Physical Review Letters; 99 2007. 10.1103/PhysRevLett.99.176103.


  • Resistive and rectifying effects of pulling gold atoms at thiol-gold nanocontacts

    R. J. C. Batista; P. Ordejón; H. Chacham; E. Artacho Physical Review B; 2007. .


  • The Calculation of Free-Energiesin Semiconductors: Defects, Transitionsand Phase Diagrams

    E. R. Hernández; A. Antonelli; L. Colombo; P. Ordejón Topics in Applied Physics; 104: 115 - 140. 2007. .


  • Transport measurements under pressure in III¿IV layered semiconductors

    A. Segura; D. Errandonea; D. Martínez García; F. J. Manjón; A. Chevy; G. Tobías; P. Ordejón; E. Canadell Physica Status Solidi (B): Basic Research; 244: 162 - 168. 2007. .


2006

  • Electron transport via local polarons at interface atoms

    Berthe, M.; Urbieta, A.; Perdigão, L.; Grandidier, B.; Deresmes, D.; Delerue, C.; Stiévenard, D.; Rurali, R.; Lorente, N.; Magaud, L.; Ordejón, P. Physical Review Letters; 97 2006. 10.1103/PhysRevLett.97.206801.


  • Methylthiolate adsorption on Au(1 1 1): Energetics, vibrational modes and STM imaging

    Gonzalez, N.; Lorente, N.; Arnau, A. Surface Science; 600: 4039 - 4043. 2006. 10.1016/j.susc.2006.01.119.


2005

  • First-principles study of structural, elastic, and bonding properties of pyrochlores

    J.M. Pruneda; Emilio Artacho Physical Review B - Condensed Matter and Materials Physics; 2005. .


  • Self-doped titanium oxide thin films for efficient visible light photocatalysis: An example: Nonylphenol photodegradation

    Justicia, I.; Garcia, G.; Vázquez, L.; Santiso, J.; Ordejón, P.; Battiston, G.; Gerbasi, R.; Figueras, A. Sensors and Actuators, B: Chemical; 109: 52 - 56. 2005. 10.1016/j.snb.2005.03.021.


2004

  • Intrinsic point defects and volume swelling in ZrSiO4 under irradiation

    J. M. Pruneda; T. D. Archer; Emilio Artacho Physical Review B - Condensed Matter and Materials Physics; 2004. .


  • Short-range repulsive interatomic interactions in energetic processes in solids

    J. M. Pruneda; Emilio Artacho Physical Review B - Condensed Matter and Materials Physics; 2004. .