A polarizable reactive force field for water to enable molecular dynamics simulations of proton transport

A new polarizable water model is developed for molecular dynamics (MD) simulations of the proton transport process. The interatomic potential model has three important submodels corresponding to electrostatic interactions, making and breaking of covalent bonds, and treatment of electron exchange and correlation through a van der Waals potential. A polarizable diffuse charge density function was used to describe Coulombic interactions between atoms. Most of the model parameters were obtained from ab initio data for a lone water molecule. Molecules respond realistically to their electrochemical environment by the use of coupled fluctuating charge and fluctuating dipole dynamics, which controlled the charge density. The main purpose of the work is to develop a general model and framework for future studies, though some validation work was performed here. We applied the model to a MD simulation study of bulk properties of liquid water at room temperature and model gave good agreement with thermodynamic and transport properties at the same conditions. The model was then applied to a preliminary study of proton transfer, in which multiple proton transfer events were observed, though the rate of proton transfer was under-predicted by a factor of 5.