Pressure-induced decomposition of solid hydrogen sulfide

Solid hydrogen sulfide is a typical molecular crystal, but its stability under pressure remains controversial. In particular, the recent experimental discovery of high-pressure superconductivity at 190 K in an H2S sample (arXiv:1412.0460) inspired efforts to revalidate this controversial issue, the pressure at which H2S decomposes and the resultant decomposition products urgent need to be evaluated. In this paper we performed an extensive structural study on different stoichiometries of HnS with n > 1 under high pressure using ab initio calculations. Our results show that H2S is stable below 43 GPa and at elevated pressure it decomposes into H3S and sulfur. H3S is stable at least up to 300 GPa, while other H-rich compounds, including H4S, H5S, and H6S, are unstable in the pressure range of this study.