Staff directory

Francesca Costanzo

Postdoctoral Researcher
Theory and Simulation



  • Structure evolution of mononuclear tungsten and molybdenum species in the protonation process: Insight from FPMD and DFT calculations

    Zhang N., Yi H., Zeng D., Zhao Z., Wang W., Costanzo F. Chemical Physics; 502: 77 - 86. 2018. 10.1016/j.chemphys.2018.01.009.

    In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4 −) may partially exist as a five-coordinated WO3(OH)(H2O)− species except for the four-coordinated WO3(OH)− species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol−1) for the WO3(OH)(H2O)− and WO3(OH)− species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)− species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO4 2− is more easily protonated than the MoO4 2− anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy. © 2018 Elsevier B.V.


  • Modeling surface motion effects in N2 dissociation on W(110): Ab initio molecular dynamics calculations and generalized Langevin oscillator model

    Nattino F., Galparsoro O., Costanzo F., Díez Muiño R., Alducin M., Kroes G.-J. Journal of Chemical Physics; 144 (24, 244708) 2016. 10.1063/1.4954773. IF: 2.894

    Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics. © 2016 Author(s).