Structure and dynamics of liquid sulphur

Abstract

First-principles molecular dynamics calculations based on density-functional theory have been used to predict the structure, vibrational spectrum, and dynamics of liquid sulphur over a wide temperature range. The calculated structure factor is in excellent agreement with that derived from neutron diffraction experiments. At low temperature, the liquid structure is found to consist primarily of ${S}_{8}$ rings. The theoretical calculations provide important structural information that may not be possible to extract from experiment. The structure at high temperatures and/or after photoexcitation is found to consist of chains of varying lengths resulting from the breakup of the ${S}_{8}$ rings. Upon quenching, longer helical chains and cross linkages are observed indicating the initial stage of polymerization. The self-diffusion constant of liquid sulphur first increases slowly reflecting the interpenetrating chains and rings but increases rapidly as the rings break up into smaller chains.