A local harmonic study of clusters of water and methane

In previous work we have extended the local harmonic model (LHM) to molecul ar 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 suc h application: the study of cluster growth towards nucleation. A range of c luster sizes has been studied from 20 to 184 water molecules. Free energy m inimisation has been applied using the LMHM and the geometry of the resulti ng clusters compared to the gas hydrate crystal geometry. Using composite c hemical potentials for the solid, gas and interfacial phases a method has b een devised to estimate the critical cluster size during nucleation.