First-principles molecular dynamics simulations at solid-liquid interfaces with a continuum solvent

VERÓNICA M. SÁNCHEZ, MARIELA SUED, DAMIÁN A. SCHERLIS

JOURNAL OF CHEMICAL PHYSICS

American Institute of Physics

Año: 2009 vol. 131 p. 174108 - 174118

0021-9606

Continuum solvent models have become a standard techniquein the context of electronic structure calculations, yet, no implementationshave been reported capable to perform molecular dynamics at solid-liquid interfaces.We propose here such a continuum approach in a DFT framework, using plane-waves basis setsand periodic boundary conditions. Our work stems from a recent modeldesigned for Car-Parrinello simulations of quantum solutes in a dielectric medium[J. Chem. Phys. 124, 74103 (2006)], forwhich the permittivity of the solvent is defined as a function of the electronicdensity of the solute. This strategy turns out to be inadequate for systems extended in two dimensions:the dependence of the dielectric functionon the electronic density introduces a new term in the Kohn-Sham potentialwhich becomes unphysically large at the interfacial region,seriously affecting the convergence of the self-consistent calculations.If the dielectric medium is properly redefined as a function ofthe atomic coordinates, a good convergence is obtained and the constant of motionis conserved during the molecular dynamics simulations.The Poisson problem is solved using a multigrid method, and in this wayCar-Parrinello molecular dynamics simulationsof solid-liquid interfaces can be performed at a very moderate computational cost.This scheme is employed to investigate the acid-base equilibrium at the TiO2-water interface.The aqueous behavior of titania surfaces has stimulated a large amount of experimental research,but many open questions remain concerning the molecular mechanisms determining thechemistry of the interface. Here we make an attempt to answer some of them,putting to the test our continuum model.