(222d) Reactive Molecular Dynamics Simulation of Liquid Water and Ice Crystal (Ice-1h)  Using a New Generation of Reactive Force Fields Based on Polarized Charge Distributions and Valance Bond Concepts

Water is probably the most important molecule to biological systems. Although it has a simple molecular structure, it is considered to be one of the most complex substances. Particular properties of water such as hydrogen bond and polarization effects are responsible for its complex behaviors. Despite of extensive atomistic simulations that have been performed during last decades, there is a growing interest to improve water potentials to describe various phenomena.

Accurately describing the electrostatic interaction between water molecules has been a longstanding challenge due to polarization effects. To address this problem, we propose a new generation of reactive force field based on polarized charge distribution (PQEq) and valance bond concepts. Our potential model allows an accurate description of the local polarization needed to describe dynamic dielectric properties of water. In PQEq methodology each atom is represented by a variable charge plus two fixed charges (core and shell), modeled with a Gaussian charge distribution. This enables the charges to evolve in response to the dynamics while including damping. In addition, in our new approach we use valence bond concepts to understand and simulate proton solvation and transport in water. These together provide all essential ingredients to model various dissociation pathways and formation of chemical bonds in water simulations.

Here, we first validate our model by describing the experimental density and equation of state of the H₂O crystal (ice-1h). We also compare the H₂O molecule and H₂O dimer dissociations with the best available quantum mechanics computations.

We also report reactive molecular dynamics of bulk water and Ice-1h crystal for large time and size scales to study structural and dynamical properties of water such as melting point, phase diagram, dielectric constants, etc. We validate our results by comparing them with available experimental data.