Multistate Empirical Valence Bond Model for Proton Transport in Water

A multistate empirical valence bond (MS-EVB) model for describing proton transport in aqueous systems is presented. In this approach the electrostatic interaction of the solvent water molecules with an exchange charge distribution is explicitly included in the off-diagonal elements of the EVB Hamiltonian. The MS-EVB model is parametrized to reproduce geometrical and energetic quantities of selected H3O+·(H2O)N clusters. The obtained geometries, formation energies, and energy barriers are in excellent agreement with results from high-level ab initio calculations. It is furthermore applied in a classical molecular dynamics simulation of condensed-phase water with an excess proton in order to estimate the proton-transfer rate.