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

Abstract

In this work the path integral formulation for rigid rotors, proposed by Müser and Berne [Phys. Rev. Lett. 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.

Keywords:

• path integral simulations
• water
• thermodynamics
• Monte Carlo

Acknowledgements

This work was funded by grants FIS2010-16159, FIS2010-15502 and FIS2009-12721-C04-04 of Dirección General de Investigación, S2009/ESP-1691 of Comunidad Autónoma de Madrid and 200980I099 of CSIC. Useful discussions with Prof. J.L.F. Abascal are gratefully acknowledged.