A configuration bias Monte Carlo method for water

Abstract

A configuration bias Monte Carlo (CBMC) procedure suitable for the insertion and deletion of water molecules (SPC/E) in grand canonical and Gibbs ensemble Monte Carlo (GEMC) simulations under ambient conditions is presented. This CBMC technique involves sampling a number of orientations of the molecule at the chosen site and selecting one with a probability proportional to its Boltzmann weight. The Swendsen–Wang technique is used to reject improbable insertions or deletions before performing expensive CBMC calculations. This approach yields significant gains in efficiency and should be applicable to many other systems. Water molecules are frequently inserted and deleted in the same locations indicating that the overall acceptance rate for such moves is somewhat misleading. A better measure is to only consider deletions of molecules that have remained in the system for a sufficiently long time. Based upon this measure insertions and deletions should be attempted at least as often as displacements in grand canonical Monte Carlo simulations of water.