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.