Publications
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A First-Principles Investigation on the Electronic and Mechanical Properties of 1T TiSe2Multilayers for Energy Storage
Antonio J.E., Cervantes J.M., Rosas-Huerta J.L., Pilo J., Carvajal E., Escamilla R. Journal of the Electrochemical Society; 168 (3, 030531) 2021. 10.1149/1945-7111/abed29. IF: 4.316
In this work, the electronic and mechanical properties of bulk TiSe2 were studied, and the effects of confinement on the compound, into mono-, bi-, and tri-layered systems, on the electronic and mechanical properties using DFT-based calculations within the Generalized Gradient Approximation (GGA) using Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Lithium atoms were placed at different adsorption sites of the TiSe2 monolayer to study the consequences on the electronic and mechanical properties and to identify the most favourable adsorption site for Li in the TiSe2 systems. Mono -, bi-, and tri-layered systems have associated a metallic behaviour, similar to the bulk material. Young's modulus for mono-, bi-, and tri-layered systems show similar behaviour to the bulk case. On the other hand, monolayers with Li are metallic when Li atoms are placed at the surface; and this behaviour could be favourable to facilitate electronic transport by the monolayer. Finally, the mechanical properties analysis supported that the better adsorption sites are those labelled as Top and Hollow. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
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Addressing the theoretical and experimental aspects of low-dimensional-materials-based fet immunosensors: A review
Martins E.F., Pinotti L.F., Silva C.C.C., Rocha A.R. Chemosensors; 9 (7, 162) 2021. 10.3390/chemosensors9070162. IF: 3.398
Electrochemical immunosensors (EI) have been widely investigated in the last several years. Among them, immunosensors based on low-dimensional materials (LDM) stand out, as they could provide a substantial gain in fabricating point-of-care devices, paving the way for fast, precise, and sensitive diagnosis of numerous severe illnesses. The high surface area available in LDMs makes it possible to immobilize a high density of bioreceptors, improving the sensitivity in biorecognition events between antibodies and antigens. If on the one hand, many works present promising results in using LDMs as a sensing material in EIs, on the other hand, very few of them discuss the fundamental interactions involved at the interfaces. Understanding the fundamental Chemistry and Physics of the interactions between the surface of LDMs and the bioreceptors, and how the operating conditions and biorecognition events affect those interactions, is vital when proposing new devices. Here, we present a review of recent works on EIs, focusing on devices that use LDMs (1D and 2D) as the sensing substrate. To do so, we highlight both experimental and theoretical aspects, bringing to light the fundamental aspects of the main interactions occurring at the interfaces and the operating mechanisms in which the detections are based. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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Assessing Nickel Titanium Binary Systems Using Structural Search Methods and Ab Initio Calculations
Lang L., Payne A., Valencia-Jaime I., Verstraete M.J., Bautista-Hernández A., Romero A.H. Journal of Physical Chemistry C; 125 (2): 1578 - 1591. 2021. 10.1021/acs.jpcc.0c10453. IF: 4.126
Nickel titanium, also know as nitinol, is a prototypical shape memory alloy, a property intimately linked to a phase transition in the microstructure, which allows the meso/macroscopic sample shape to be recovered after thermal cycling. Not much is known about the other alloys in this binary system, which prompted our computational investigation of other compositions. In this work, structures are found by probing the potential energy surfaces of NiTi binary systems using a minima hopping method, in combination with ab initio electronic structure calculations. We find stable structures in 34 different stoichiometries and calculate derived physical properties of the low energy phases. From the results of this analysis a new convex hull is formed that is lower in energy than those in the Materials Project and Open Quantum Materials Databases. Two previously unreported phases are discovered for the NiTi2 and Ni5Ti compositions, and two metastable states in NiTi and NiTi2 shows signs of negative linear compression and negative Poisson ratio, respectively. ©
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Atomic-scale defects restricting structural superlubricity: Ab initio study on the example of the twisted graphene bilayer
Minkin A.S., Lebedeva I.V., Popov A.M., Knizhnik A.A. Physical Review B; 104 (7, 075444) 2021. 10.1103/PhysRevB.104.075444. IF: 4.036
The potential energy surface (PES) of interlayer interaction of twisted bilayer graphene with vacancies in one of the layers is investigated via density functional theory (DFT) calculations with van der Waals corrections. These calculations give a non-negligible magnitude of PES corrugation of 28 meV per vacancy and barriers for relative sliding of the layers of 7-8 meV per vacancy for the moiré pattern with coprime indices (2,1) (twist angle 21.8). At the same time, using the semiempirical potential fitted to the DFT results, we confirm that twisted bilayer graphene without defects exhibits superlubricity for the same moiré pattern and the magnitude of PES corrugation for the infinite bilayer is below the calculation accuracy. Our results imply that atomic-scale defects restrict the superlubricity of two-dimensional layers and can determine static and dynamic tribological properties of these layers in a superlubric state. We also analyze computationally cheap approaches that can be used for modeling of tribological behavior of large-scale systems with defects. The adequacy of using state-of-the-art semiempirical potentials for interlayer interaction and approximations based on the first spatial Fourier harmonics for the description of interaction between graphene layers with defects is discussed. © 2021 American Physical Society.
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Basic aspects of the charge density wave instability of transition metal trichalcogenides NbSe3and monoclinic-TaS3
Guster B., Pruneda M., Ordejón P., Canadell E., Pouget J.-P. Journal of Physics Condensed Matter; 33 (48, 485401) 2021. 10.1088/1361-648X/ac238a. IF: 2.333
NbSe3 and monoclinic-TaS3 (m-TaS3) are quasi-1D metals containing three different types of chains and undergoing two different charge density wave Peierls transitions at TP1 and TP2 associated with type III and type I chains, respectively. The nature of these transitions is discussed on the basis of first-principles DFT calculation of their Fermi surface (FS) and electron-hole response function. Because of the stronger inter-chain interactions, the FS and electron-hole response function are considerably more complex for NbSe3 than m-TaS3; however a common scenario can be put forward to rationalize the results. The intra-chain inter-band nesting processes dominate the strongest response for both type I and type III chains of the two compounds. Two well-defined maxima of the electron-hole response for NbSe3 are found with the (0a∗, 0c∗) and (1/2a∗, 1/2c∗) transverse components at TP1 and TP2, respectively, whereas the second maximum is not observed for m-TaS3 at TP2. Analysis of the different inter-chain coupling mechanisms leads to the conclusion that FS nesting effects are only relevant to set the transverse a∗ components in NbSe3. The strongest inter-chain Coulomb coupling mechanism must be taken into account for the transverse coupling along c∗ in NbSe3 and along both a∗ and c∗ for m-TaS3. Phonon spectrum calculations reveal the formation of a giant 2kF Kohn anomaly for m-TaS3. All these results support a weak coupling scenario for the Peierls transition of transition metal trichalcogenides. © 2021 IOP Publishing Ltd.
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Coexistence of vortex arrays and surface capillary waves in spinning prolate superfluid He 4 nanodroplets
Pi M., Escartín J.M., Ancilotto F., Barranco M. Physical Review B; 104 (9, 094509) 2021. 10.1103/PhysRevB.104.094509. IF: 4.036
Within density functional theory, we have studied the interplay between vortex arrays and capillary waves in spinning prolate He4 droplets made of several thousand helium atoms. Surface capillary waves are ubiquitous in prolate superfluid He4 droplets, and depending on the size and angular momentum of the droplet, they may coexist with vortex arrays. We have found that the equilibrium configuration of small prolate droplets is vortex free, evolving towards vortex hosting as the droplet size increases. This result is in agreement with a recent experiment [O'Connell, Phys. Rev. Lett. 124, 215301 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.215301] that disclosed that vortex arrays and capillary waves coexist in the equilibrium configuration of very large drops. In contrast to viscous droplets executing rigid-body rotation, the stability phase diagram of spinning He4 droplets cannot be universally described in terms of dimensionless angular momentum and angular velocity variables: Instead, the rotational properties of superfluid helium droplets display a clear dependence on the droplet size and the number of vortices they host. © 2021 American Physical Society.
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Conducting chiral nickel(ii) bis(dithiolene) complexes: Structural and electron transport modulation with the charge and the number of stereogenic centres
Abhervé A., Mroweh N., Cauchy T., Pop F., Cui H., Kato R., Vanthuyne N., Alemany P., Canadell E., Avarvari N. Journal of Materials Chemistry C; 9 (12): 4119 - 4140. 2021. 10.1039/d1tc00439e. IF: 7.393
Nickel(ii) bis(dithiolene) complexes can provide crystalline conducting materials either in their monoanionic or neutral forms. Here we show that the use of chiral dithiolene ligands with one or two stereogenic centres, together with variation of the counter-ion in the anionic complexes, represents a powerful strategy to modulate the conducting properties of such molecular materials. The chiral ligands 5-methyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (me-dddt) and 5,6-dimethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (dm-dddt) have been generated from the thione precursors 1 and 2 which have been structurally and chiroptically characterized. Anionic Ni(ii) complexes of these two ligands with tetrabutyl-ammonium (TBA) and tetramethyl-ammonium (TMA) have been prepared and structurally characterized, suggesting that it is the nature of the counter-ion which mostly influences the solid state organization of the complexes. Both TBA and TMA radical anion salts are Mott insulators with antiferromagnetic ground state, as suggested by spin polarized DFT band structure calculations. However, the TMA salts are one order of magnitude more conducting than the TBA counterparts. The neutral materials [Ni(me-dddt)2] and [Ni(dm-dddt)2] are direct band gap semiconductors, as determined by DFT and extended Hückel band structure calculations, with their conductivity drastically increased up to 0.05-3.3 S cm-1 under the highest applied pressures of 10-11 GPa. At equivalent applied pressures the dm-dddt materials are more conducting than the me-dddt ones, in agreement with the lower calculated activation energy and larger bands dispersion for the former. This trend follows the structural change when going from one to two methyl substituents, since the packing and intermolecular interactions are completely different between [Ni(dm-dddt)2] and [Ni(me-dddt)2], the packing of the latter being related to the one of the achiral parent [Ni(dddt)2]. Subtle differences of conductivity are also observed within both series of neutral complexes between the enantiopure and racemic forms. This represents the first series of chiral nickel bis(dithiolene) complexes which shows modulation of the conducting properties with the number of stereogenic centres, the conductivity, measured on single crystals, strongly increasing upon applying hydrostatic pressure. This journal is © The Royal Society of Chemistry.
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DFT Electronic Properties and Synthesis Thermodynamics of LixLa1-xTiO3Electrolytes for Li-Ion Batteries
Cervantes J.M., Pilo J., Rosas-Huerta J.L., Antonio J.E., Munoz H., Oviedo-Roa R., Carvajal E. Journal of the Electrochemical Society; 168 (8, 080516) 2021. 10.1149/1945-7111/ac1a52. IF: 4.316
Lithium lanthanum titanate perovskites Li x La1-x TiO3 (LLTO) are promising solid-electrolytes for Li-ion batteries. We studied, in the Density-Functional-Theory framework, the thermodynamic stability and the electronic and magnetic properties of LLTO, as bulk materials and as thin slabs with (001) exposed surfaces. Results show that LaTiO3 (LTO) exhibits semiconductor behavior and G-type antiferromagnetic order (AFMG), whereas the TiO2-terminated LTO slab is a semiconductor with ferromagnetic (FM) order. Contrasting, the LTO slab exposing a LaO-terminated surface is a conductor with AFMG ordered Ti cations' magnetic moments (MMs), but at the surface there are some FM ordered MMs (La atoms). LLTO bulk electrolyte is a semiconductor (x = 0.25) or insulator (x = 0.50). The LLTO slab is a FM (non-magnetic) conductor (TiO2 (LiO)-terminated surface) or a FM semiconductor (LaO-terminated). Besides, the stability of the LLTO bulk and slabs structures was analyzed, as well as the slabs' preferences for LiO, LaO or TiO2 ends. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
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Exploring the elastic and electronic properties of chromium molybdenum diboride alloys
Dovale-Farelo V., Tavadze P., Verstraete M.J., Bautista-Hernández A., Romero A.H. Journal of Alloys and Compounds; 866 (158885) 2021. 10.1016/j.jallcom.2021.158885. IF: 5.316
We perform first-principles calculations to study the structural, mechanical, thermal, electronic, and magnetic properties of Cr1−xMoxB2 for x = 0.25, 0.33, 0.50, 0.67 and 0.75. Based on structural search methods, we determine the ground-state structure for each concentration. The ternaries are either monoclinic (x = 0.25, 0.75) or trigonal (x = 0.33, 0.50, 0.67). The calculated mechanical properties reveal that the strength of Cr1−xMoxB2 is maximized for x = 0.50. Cr0.5Mo0.5B2 exhibits excellent mechanical properties (B = 298 GPa, Y = 558 GPa, G = 235 Gpa, ν = 0.19, Hv =27 GPa), surpassing those of β-MoB2 at a lower cost. All of these ternaries are hard alloys with Vickers hardness greater than 24 GPa. Chemical bonding analysis demonstrates that the strength of the new compounds is related to the alternating planar and buckled B-B layers, as well as the strong TM-B bonds. The enhanced strength of Cr0.5Mo0.5B2 is a consequence of the high density of strong interlayer Cr-Mo metallic bonds around the Fermi level. © 2021 Elsevier B.V.
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Giant thermoelectric figure of merit in multivalley high-complexity-factor LaSO
Farris R., Ricci F., Casu G., Dahliah D., Hautier G., Rignanese G.-M., Fiorentini V. Physical Review Materials; 5 (12, 125406) 2021. 10.1103/PhysRevMaterials.5.125406. IF: 3.989
We report a giant thermoelectric figure of merit ZT (up to six at 1100 K) in n-doped lanthanum oxysulphate LaSO. Thermoelectric coefficients are computed from ab initio bands within Bloch-Boltzmann theory in an energy-, chemical potential-, and temperature-dependent relaxation time approximation. The lattice thermal conductivity is estimated from a model employing the ab initio phonon and Grüneisen-parameter spectrum. The main source of the large ZT is the significant power factor which correlates with a large band complexity factor. We also suggest a possible n-type dopant for the material based on ab initio calculations. © 2021 American Physical Society.
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Localized electronic vacancy level and its effect on the properties of doped manganites
Juan D., Pruneda M., Ferrari V. Scientific Reports; 11 (1, 6706) 2021. 10.1038/s41598-021-85945-5. IF: 4.380
Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites La (1 - x)Sr xMnO 3, varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range (0.2<x<0.5). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites (x∼1/3), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds. © 2021, The Author(s).
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Metallic Diluted Dimerization in VO2 Tweeds
Sandiumenge F., Rodríguez L., Pruneda M., Magén C., Santiso J., Catalan G. Advanced Materials; 33 (9, 2004374) 2021. 10.1002/adma.202004374. IF: 30.849
The observation of electronic phase separation textures in vanadium dioxide, a prototypical electron-correlated oxide, has recently added new perspectives on the long standing debate about its metal–insulator transition and its applications. Yet, the lack of atomically resolved information on phases accompanying such complex patterns still hinders a comprehensive understanding of the transition and its implementation in practical devices. In this work, atomic resolution imaging and spectroscopy unveils the existence of ferroelastic tweed structures on ≈5 nm length scales, well below the resolution limit of currently used spectroscopic imaging techniques. Moreover, density functional theory calculations show that this pretransitional fine-scale tweed, which on average looks and behaves like the standard metallic rutile phase, is in fact weaved by semi-dimerized chains of vanadium in a new monoclinic phase that represents a structural bridge to the monoclinic insulating ground state. These observations provide a multiscale perspective for the interpretation of existing data, whereby phase coexistence and structural intermixing can occur all the way down to the atomic scale. © 2021 Wiley-VCH GmbH
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Multiscale modeling strategy to solve fullerene formation mystery
Popov A.M., Lebedeva I.V., Vyrko S.A., Poklonski N.A. Fullerenes Nanotubes and Carbon Nanostructures; 29 (10): 755 - 766. 2021. 10.1080/1536383X.2021.1900124. IF: 1.869
Since fullerene formation occurs under conditions where direct observation of atomic-scale reactions is not possible, modeling is the only way to reveal atomistic mechanisms which can lead to selection of abundant fullerene isomers (like C60-Ih). In the present paper we review the results obtained for different atomistic mechanisms by various modeling techniques. Although it seems that atomic-scale processes related to odd fullerenes (such as growth by consecutive insertions of single carbon atoms and rearrangements of the sp2 structure promoted by extra sp atoms) provide the main contribution to selection of abundant isomers, at the moment there is no conclusive evidence in favor of any particular atomistic mechanism. Thus, the following multiscale modeling strategy to solve the mystery of the high yield of abundant fullerene isomers is suggested. On the one hand, sets of reactions between fullerene isomers can be described using theoretical graph techniques. On the other hand, reaction schemes can be revealed by classical molecular dynamics simulations with subsequent refinement of the activation barriers by ab initio calculations. Based on the reaction sets with the reaction probabilities derived in this way, the different atomistic mechanisms of abundant fullerene isomer selection can be compared using kinetic models. © 2021 Taylor & Francis Group, LLC.
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Optical Signatures of Defect Centers in Transition Metal Dichalcogenide Monolayers
de Melo P.M.M.C., Zanolli Z., Verstraete M.J. Advanced Quantum Technologies; 4 (3, 2000118) 2021. 10.1002/qute.202000118. IF: 0.000
Even the best quality 2D materials have non-negligible concentrations of vacancies and impurities. It is critical to understand and quantify how defects change intrinsic properties, and use this knowledge to generate functionality. This challenge can be addressed by employing many-body perturbation theory to obtain the optical absorption spectra of defected transition metal dichalcogenides. Herein metal vacancies, which are largely unreported, show a larger set of polarized excitons than chalcogenide vacancies, introducing localized excitons in the sub-optical-gap region, whose wave functions and spectra make them good candidates as quantum emitters. Despite the strong interaction with substitutional defects, the spin texture and pristine exciton energies are preserved, enabling grafting and patterning in optical detectors, as the full optical-gap region remains available. A redistribution of excitonic weight between the A and B excitons is visible in both cases and may allow the quantification of the defect concentration. This work establishes excitonic signatures to characterize defects in 2D materials and highlights vacancies as qubit candidates for quantum computing. © 2021 The Authors. Advanced Quantum Technologies published by Wiley-VCH GmbH
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Spontaneous interlayer compression in commensurately stacked van der Waals heterostructures
Pike N.A., Dewandre A., Chaltin F., Garcia Gonzalez L., Pillitteri S., Ratz T., Verstraete M.J. Physical Review B; 103 (23, 235307) 2021. 10.1103/PhysRevB.103.235307. IF: 4.036
Interest in layered two-dimensional materials, particularly stacked heterostructures of transition-metal dichalcogenides, has led to the need for a better understanding of the structural and electronic changes induced by stacking. Here, we investigate the effects of idealized heterostructuring, with periodic commensurate stacking, on the structural, electronic, and vibrational properties, when compared to the counterpart bulk transition-metal dichalcogenide. We find that in heterostructures with dissimilar chalcogen species there is a strong compression of the interlayer spacing, compared to the bulk compounds. This compression of the heterostructure is caused by an increase in the strength of the induced polarization interaction between the layers, but not a full charge transfer. We argue that this effect is real, not due to the imposed commensurability, and should be observable in heterostructures combining different chalcogens. Interestingly, we find that incommensurate stacking of Ti-based dichalcogenides can lead to the stabilization of the charge-density wave phonon mode, which is unstable in the 1T phase at low temperature. Mixed Ti- and Zr-based heterostructures are still dynamically unstable, but TiS2/ZrS2 becomes ferroelectric. © 2021 American Physical Society.
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Spontaneous phase segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 heteroepitaxy
Wang L., Yang Z., Yin X., Taylor S.D., He X., Tang C.S., Bowden M.E., Zhao J., Wang J., Liu J., Perea D.E., Wangoh L., Wee A.T.S., Zhou H., Chambers S.A., Du Y. Science Advances; 7 (10, eabe2866) 2021. 10.1126/sciadv.abe2866. IF: 14.143
Recent discovery of superconductivity in Nd0.8Sr0.2NiO2 motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric R1−xSrxNiO3 thin films over a range of x has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO3. Here, we show that spontaneous phase segregation occurs while depositing SrNiO3 thin films on perovskite oxide substrates by molecular beam epitaxy. Two coexisting oxygen-deficient Ruddlesden-Popper phases, Sr2NiO3 and SrNi2O3, are formed to balance the stoichiometry and stabilize the energetically preferred Ni2+ cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the instability in perovskite structured SrNiO3 and the tendency of transition metal cations to form their most stable valence (i.e., Ni2+ in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying emerging phenomena in nickel-based oxides. Copyright © 2021 The Authors, some rights reserved;
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Structural and magnetic phase diagram of epitaxial La0.7Sr0.3MnO3from first principles
Pilo J., Pruneda M., Bristowe N.C. Electronic Structure; 3 (2, 024001) 2021. 10.1088/2516-1075/abe6af. IF: 0.000
ABO3perovskites host a huge range of symmetry lowering structural distortions, each of which can tune, or even switch on or off, different functional properties due to the strong coupling between the lattice, spin and charge degrees of freedom in these materials. The sheer number of different meta-stable structures present in perovskites creates a challenge for materials design via theory and simulation. Here, we tackle this issue using a first principles structure searching method on a prototypical half-metallic perovskite, La0.7Sr0.3MnO3, to predict how epitaxial strain can engineer structural and magnetic properties.We reveal a rich structural phase diagram through strain engineering in which the octahedral tilt pattern, and hence the crystal symmetry, is altered from the bulk.We show how the low-symmetry of the various phases in turn induces new structural modes, an increase in the magnetic anisotropy energy, and weak antiferromagnetic spin-canting. © 2021 The Author(s).
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TB2J: A python package for computing magnetic interaction parameters
He X., Helbig N., Verstraete M.J., Bousquet E. Computer Physics Communications; 264 (107938) 2021. 10.1016/j.cpc.2021.107938. IF: 4.390
We present TB2J, a Python package for the automatic computation of magnetic interactions, including exchange and Dzyaloshinskii–Moriya, between atoms of magnetic crystals from the results of density functional calculations. The program is based on the Green's function method with the local rigid spin rotation treated as a perturbation. As input, the package uses the output of either Wannier90, which is interfaced with many density functional theory packages, or of codes based on localized orbitals. One of the main interests of the code is that it requires only one first-principles electronic structure calculation in the non-relativistic case (or three in the relativistic case) and from the primitive cell only to obtain the magnetic interactions up to long distances, instead of first-principles calculations of many different magnetic configurations and large supercells. The output of TB2J can be used directly for the adiabatic magnon band structure and spin dynamics calculations. A minimal user input is needed, which allows for easy integration into high-throughput workflows. Program summary: Program Title: TB2J CPC Library link to program files: https://doi.org/10.17632/dm45fcn69d.1 Developer's repository link: https://github.com/mailhexu/TB2J Code Ocean capsule: https://codeocean.com/capsule/6486145 Licensing provisions: BSD 2-clause Programming language: Python Nature of problem: TB2J is a package for the computing of parameters in the extended Heisenberg model of the magnetic interaction, including the isotropic exchange, anisotropic exchange and Dzyaloshinskii–Moriya interactions from first principles result. It can make use of the Wannier function Hamiltonian, which can be constructed from many first principles codes, or localized orbital based codes. Solution method: It uses the magnetic force theorem and takes the rigid spin rotation as a perturbation to the electronic structure. The energy variation is calculated from the Green's functions from tight-binding like Hamiltonian based on Wannier functions or localized orbitals. Additional comments including restrictions and unusual features: Isotropic exchange, anisotropic exchange, and Dzyaloshinskii–Moriya interactions can all be computed with the input of many DFT codes through the interface of Wannier90, or directly from localized orbital codes. The magnetic interaction parameters up to any distance can be computed from one DFT calculation. A minimum user-input is required which provides a black-box like experience. It generates output for several spin dynamics codes and thus bridges the first principles electronic structure simulation with the large scale spin dynamics simulation. © 2021 Elsevier B.V.
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Validity of the on-site spin-orbit coupling approximation
Cuadrado R., Robles R., García A., Pruneda M., Ordejón P., Ferrer J., Cerdá J.I. Physical Review B; 104 (19, 195104) 2021. 10.1103/PhysRevB.104.195104. IF: 4.036
Spin-orbit coupling (SOC) is generally understood as a highly localized interaction within each atom, whereby core electrons holding large J splittings transfer the SOC to the valence electrons of the same atom, while their direct impact on neighbor valence orbitals is usually small. Seivane and Ferrer [Phys. Rev. Lett. 99, 183401 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.183401] proposed an approach within a tight-binding type ab initio framework assuming that the transfer of SOC from core to valence orbitals only takes place when both are on the same atom, leading to the so-called on-site approximation, which then has been successfully applied to a variety of systems. In this work we thoroughly test its general validity by confronting SOC related properties such as spin splittings, spin textures, or magnetic anisotropies calculated under the on-site approximation versus the more general approach where all the contributions to the SOC, including three-center integrals, are explicitly included. After considering a variety of systems with different dimensionalities, all presenting a strong SOC, we conclude that although the on-site approximation often provides accurate results, it breaks down in some systems where 5d electrons are close to the Fermi level due to their strong SOC and moderately large spatial extension. Furthermore, there are a few examples where subtle inaccuracies lead to qualitatively wrong conclusions, the most clear case being the doping of the topological surface state in Bi2Se3(0001). Finally, magnetic anisotropy energies calculated under this approximation tend to be underestimated. © 2021 American Physical Society.
