Quantum–Classical Simulation of Proton Migration in Water

Abstract

AbstractProton transport in water is treated within a mixed quantum–classical molecular dynamics scheme. Therein the migration of a positive charge is treated as a two‐step process: (i) the displacement of a hydronium ion, followed by (ii) proton transfer between a hydronium ion and an adjacent water molecule. Both the hydronium ion and the water molecules are treated as flexible molecules. In the H5O2+‐complex, the proton no longer belongs to a single water molecule, but is delocalized between the two oxygen atoms. The proton transfer is treated quantum mechanically as a function of a transfer coordinate within a single complex. The quantum description is changed to another pair of water molecules after strong proton localization to one of the water molecules in the complex and according to distance criteria with respect to adjacent water molecules. It is demonstrated that the proposed formalism is well suited for an effective simulation of the proton migration in water. In particular, the lifetimes of Eigen complexes and the proton diffusion coefficient (as obtained from simulations) are in very good agreement with corresponding experimental data.