Elucidating the role of many-body forces in liquid water. I. Simulations of water clusters on the VRT(ASP-W) potential surfaces

Abstract

Abstract In the quest for a quantitative simulation of liquid water it appears the potential energy of the interaction of water molecules converges very rapidly and may be described adequately by only two- and three-body terms. Measurements of vibration-rotation tunneling (VRT) splittings for water dimers have provided data for fitting an anisotropic site potential with Woermer dispersion (ASPW) to provide a series of highly detailed potential energy surfaces. The expressions for these surfaces include terms corresponding to electrostatic interaction, two-body exchange repulsion, two-body dispersion, and many-body induction. In this paper the authors report an investigation of the suitability of these surfaces and several others for predicting the vibrational ground-state properties of water clusters ranging from the trimer to the hexamer. The calculations were carried out with diffusion Q:tvIC to determine cluster properties, the structures and, in particular, the vibrational average rotational constants for direct comparison with experimentally measured values. The ground-state properties were determined in runs for 1000 walkers with 15,000-20,000 time steps after equilibration. Histograms of configurations were used for calculating the internal tensors leading to the rotational constants.