A molecular dynamics simulation study of the plastic crystalline phase of sulphur hexafluoride

Abstract

A molecular dynamics simulation study of the plastic crystalline phase of SF6 is reported. Various equilibrium properties have been measured and, where possible, compared with corresponding experimental measurements. The form of the molecular orientational distribution function has been obtained and is found to be in good agreement with that determined in a recent neutron scattering study. Information concerning the single-molecule dynamics has been obtained from calculations of linear and angular velocity autocorrelation functions, and it has been shown that the SF6 molecules undergo hindered rotation. The existence of coupling between the translational and rotational motions has been demonstrated, and it is shown how the behaviour of the plastic crystal is related to the form of the intermolecular potential. In addition, a transition to a trigonal low-temperature crystal phase at 80K has been observed, and the structure of this phase has been identified and found to be in good agree with experimental results. The calculations have been performed using a large parallel-array processor, and features of the simulation algorithms that reflect the architecture of such a computer are discussed.