A local harmonic study of clusters of water and methane

Abstract

In previous work we have extended the local harmonic model (LHM) to molecular systems and applied it in a study of the bulk properties of gas hydrates. This local molecular harmonic model (LMHM) has several other interesting applications in the study of gas hydrates. In this paper we present one such application: the study of cluster growth towards nucleation. A range of cluster sizes has been studied from 20 to 184 water molecules. Free energy minimisation has been applied using the LMHM and the geometry of the resulting clusters compared to the gas hydrate crystal geometry. Using composite chemical potentials for the solid, gas and interfacial phases a method has been devised to estimate the critical cluster size during nucleation.