A first principles simulation of rigid water

TL;DR

This paper demonstrates that using a rigid water molecule approximation in Car-Parrinello simulations improves agreement with experimental structural and dynamic properties, enabling longer simulations of aqueous systems.

Contribution

The study introduces a rigid molecule approximation in ab initio water simulations, allowing longer time scales and better experimental agreement.

Findings

Rigid water model yields structural properties closer to experiments.

Diffusion coefficients are more accurate with the rigid model.

Enables longer simulations of aqueous solutions.

Abstract

We present the results of Car-Parrinello (CP) simulations of water at ambient conditions and under pressure, using a rigid molecule approximation. Throughout our calculations, water molecules were maintained at a fixed intramolecular geometry corresponding to the average structure obtained in fully unconstrained simulations. This allows us to use larger time steps than those adopted in ordinary CP simulations of water, and thus to access longer time scales. In the absence of chemical reactions or dissociation effects, these calculations open the way to ab initio simulations of aqueous solutions that require timescales substantially longer than presently feasible (e.g. simulations of hydrophobic solvation). Our results show that structural properties and diffusion coefficients obtained with a rigid model are in better agreement with experiment than those determined with fully flexible simulations. Possible reasons responsible for this improved agreement are discussed.