Computer Simulation of the Plastic-to-Crystalline Phase Transition in SF6

A simple but realistic model for the condensed phases of S${\mathrm{F}}_6$ gives a plastic phase at 80 K in a molecular-dynamics simulation. Equilibration of a sample of 4096 molecules at 25 K and at zero pressure results in a transition to a polycrystal. The crystal structure found is triclinic $P\overline{1}$, $Z=3\mathrm{}$, but is pseudo-orthorhombic, a result not inconsistent with recent spectroscopic measurements. It is suggested that, to avoid bias, a large size is necessary for modeling the plastic-to-crystalline phase transition.