Atomistic Simulations of the ZnO(12̅10)/Water Interface: A Comparison between First-Principles, Tight-Binding, and Empirical Methods.

Abstract

We investigate the adsorption behavior of water over the zinc oxide (12̅10) surface starting from single molecules up to bulk liquid by means of atomistic molecular dynamics simulations. We compare results obtained with density-functional theory, density-functional tight binding, and a recently developed reactive force field. The methods perform comparably up to the level of a single monolayer of adsorbed water, predicting only small differences in adsorption energies and, as a consequence, adsorption geometries. These lie within the error bars of typical quantum mechanical calculations performed with different exchange-correlation functionals. However, the discrepancies among the methods have a dramatic effect on the dissociation equilibria and the structuring of liquid water layers in contact with the surface. Especially the different treatment of electrostatic interactions via self-consistent atomic point charges appears to heavily influence the simulation outcomes. Critical comparisons with experimental studies and possibly ad hoc reparametrizations of the semiempirical functionals may thus be necessary to study phenomena such as dissolution or biomolecular adsorption at ZnO surfaces within statistically relevant time and size scales.