A molecular dynamics simulation study of the orientationally disordered phase of sulphur hexafluoride

The orientationally disordered phase of sulphur hexafluoride at 150K has been studied here using the molecular dynamics simulation technique, with particular emphasis placed on the origin and nature of the orientational disorder. A model involving the frustration of two competing intermolecular interactions that had been proposed previously has been shown to be a good description of the origin of the disorder through calculations that have given information concerning the correlations between the orientations of neighbouring molecules. It has also been shown that the disorder is dynamic rather than static in nature, and features of the molecular motion that are related to this dynamic disorder have been identified. It is suggested that some of the features of orientationally disordered crystals that have been studied might be observed experimentally in a coherent neutron scattering study, and some preliminary calculations of S(Q) are reported.