Structural change in liquid sulphur from chain polymeric liquid to atomic simple liquid under high pressure

The structural properties of liquid sulphur under high pressure up to approximately 500 GPa have been investigated by means of ab initio molecular-dynamics (MD) simulations. The obtained pair distribution functions and spatial distribution of electron density under high pressure indicate the existence of a covalent-like interaction even in the metallic state and the covalent-like interaction gradually decreases with increasing pressure. By analyzing the static structure factor, it is found that the covalent-like interaction still remains at approximately 200 GPa, and liquid sulphur has a simple liquid structure at 320 GPa and higher pressures. These results indicate that the covalent-like interaction disappears at a pressure between 200 and 320 GPa. In this study, we also estimate the pressure range of structural change in other liquid chalcogens in a similar manner as liquid S. The pressures at which liquid Se and Te have simple liquid structure are estimated to be larger than approximately 100 and 20 GPa, respectively.