Molecular dynamics study of the phase transitions in sulfur hexafluoride clusters of various size

Abstract

Molecular dynamics (MD) simulations have been performed on free clusters of sulfur hexafluoride (SF 6 ) of various size: 229, 137, and 55 molecules. Some preliminary simulations of 13-molecule clusters have also been performed. A systematic study of the melting and solid-solid transitions and the effect of cluster size on their temperature spreads was undertaken. The stable structures of the 229-, 137-, and 55-molecule clusters are bcc at elevated temperatures and C2/m monoclinic at low temperature, as in the bulk crystal. The melting transition is rounded and shifted to low temperatures when decreasing the cluster size. In the whole size range, from the thermodynamic limit down to 55 molecules, melting initiates at the surface