Molecular Dynamics Simulations of Liquid Water Structure and Diffusivity

Abstract

An ab initio force field has been constructed to study the structure and diffusivity for liquid water using molecular dynamics simulations. The potential energy data were calculated by using both the second order Moller-Plesset (MP2) perturbation theory and the coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)], together with the correlation consistent basis set up to aug-cc-pV5Z. For configuration sampling, we considered 10 dimer orientations, each with about 121 grid points. With an additional ”polarization” term, an analytical function similar to that for the well-established TIP4P model was used to represent the ab initio potential data. The simulation results were compared with those using several empirical force fields (SPC/E, TIP4P etc.) or the recent CC-pol series of ab initio force fields and also with available experimental measurements. We obtained good quantitative agreement for the atom-wise radial distribution functions and the self-diffusion coefficients over a wide range of thermodynamic conditions. This new ab initio force field can thus serve as a suitable starting point for predicting liquid water properties without priori empirical knowledge.