Pressure-induced phase transition of hydrogen sulfide at low temperature: Role of the hydrogen bond and short S-S contacts

Abstract

New phase transitions have recently been observed experimentally for ${\mathrm{H}}_{2}\mathrm{S}$ in the low-temperature and high-pressure regime. In this paper the nature of the transition between phases ${\mathrm{IV}}^{\ensuremath{'}}$ and IV is elucidated using ab initio constant pressure molecular-dynamics simulations. We show that the cell parameters do not show discontinuity at the phase boundary between phases ${\mathrm{IV}}^{\ensuremath{'}}$ and IV consistent with the experimental results. The present analysis suggests that the formation of short S-S contacts and the reformation of hydrogen-bonded network are the possible driving force of the ${\mathrm{IV}}^{\ensuremath{'}}\ensuremath{\rightarrow}\mathrm{IV}$ transition. Implications to the phase IV structure at room temperature will also be given.