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

V. M. SANCHEZ; M. SUED; D. A. SCHERLIS PEREL

JOURNAL OF CHEMICAL PHYSICS

Año: 2009 p. 1741081 - 17410810

0021-9606

Continuum solvent models have become a standard technique in the context of electronic structurecalculations, yet no implementations have been reported capable to perform molecular dynamics atsolid-liquid interfaces. We propose here such a continuum approach in a density functional theoryframework using plane-wave basis sets and periodic boundary conditions. Our work stems from arecent model designed for Car–Parrinello simulations of quantum solutes in a dielectric medium D. A. Scherlis et al., J. Chem. Phys. 124, 074103 (2006), for which the permittivity of the solvent isdefined as a function of the electronic density of the solute. This strategy turns out to be inadequatefor systems extended in two dimensions: the dependence of the dielectric function on the electronicdensity introduces a new term in the Kohn–Sham potential, which becomes unphysically large at theinterfacial region, seriously affecting the convergence of the self-consistent calculations. If thedielectric medium is properly redefined as a function of the atomic coordinates, a good convergenceis obtained and the constant of motion is conserved during the molecular dynamics simulations. ThePoisson problem is solved using a multigrid method, and in this way Car–Parrinello moleculardynamics simulations of solid-liquid interfaces can be performed at a very moderate computationalcost. 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, butmany open questions remain concerning the molecular mechanisms determining the chemistry ofthe interface. Here we make an attempt to answer some of them, putting to the test our continuummodel.