Path integral Monte Carlo simulations for rigid rotors and their application to water

TL;DR

This paper details the path integral Monte Carlo method for rigid rotors and applies it to water, highlighting the importance of quantum effects in accurately modeling water's properties, especially at low temperatures.

Contribution

It provides a detailed implementation of path integral Monte Carlo simulations for rigid rotors and demonstrates their application to water, emphasizing quantum effects.

Findings

Quantum effects are crucial for accurate water modeling at low temperatures.

Classical simulations can reproduce some properties but fail for others.

Quantum effects significantly influence the equation of state and structure of ice phases.

Abstract

In this work the path integral formulation for rigid rotors, proposed by M\"user and Berne [Phys. Rev. Lett. {\bf 77}, 2638 (1996)], is described in detail. It is shown how this formulation can be used to perform Monte Carlo simulations of water. Our numerical results show that whereas some properties of water can be accurately reproduced using classical simulations with an empirical potential which, implicitly, includes quantum effects, other properties can only be described quantitatively when quantum effects are explicitly incorporated. In particular, quantum effects are extremely relevant when it comes to describing the equation of state of the ice phases at low temperatures, the structure of the ices at low temperatures, and the heat capacity of both liquid water and the ice phases. They also play a minor role in the relative stability of the ice phases.