The phase diagram of water from quantum simulations

TL;DR

This study uses quantum simulations to calculate the water phase diagram with nuclear quantum effects, revealing a qualitative match with experimental data but with a temperature shift, and linking quantum effects to tetrahedral order.

Contribution

It introduces a method to incorporate nuclear quantum effects into water phase diagram calculations using path integral Monte Carlo and thermodynamic integration.

Findings

Phase diagram qualitatively correct with a 15-20K temperature shift

Nuclear quantum effects linked to tetrahedral order parameter

Method successfully incorporates quantum effects into classical water models

Abstract

The phase diagram of water has been calculated for the TIP4PQ/2005 model, an empirical rigid non-polarisable model. The path integral Monte Carlo technique was used, permitting the incorporation of nuclear quantum effects. The coexistence lines were traced out using the Gibbs-Duhem integration method, once having calculated the free energies of the liquid and solid phases in the quantum limit, which were obtained via thermodynamic integration from the classical value by scaling the mass of the water molecule. The resulting phase diagram is qualitatively correct, being displaced to lower temperatures by 15-20K. It is found that the influence of nuclear quantum effects are correlated to the tetrahedral order parameter.