High pressure layered structure of carbon disulfide

Abstract: Solid CS${2}$ is superficially similar to CO${2}$, with the same $Cmca$ molecular crystal structure at low pressures, which has suggested similar phases also at high pressures. We carried out an extensive first principles evolutionary search in order to identify the zero temperature lowest enthalpy structures of CS${2}$ for increasing pressure up to 200\,GPa. Surprisingly, the molecular $Cmca$ phase does not evolve into $\beta$-cristobalite as in CO${2}$, but transforms instead into phases HP2 and HP1, both recently described in high pressure SiS${2}$. HP1 in particular, with a wide stability range, is a layered $P2{1}/c$ structure characterized by pairs of edge-sharing tetrahedra, and theoretically more robust than all other CS${2}$ phases discussed so far. Its predicted Raman spectrum and pair correlation function agree with experiment better than those of $\beta$-cristobalite, and further differences are predicted between their respective IR spectra. The band gap of HP1-CS${2}$ is calculated to close under pressure yielding an insulator-metal transition near 50 GPa in agreement with experimental observations. However, the metallic density of states remains modest above this pressure, suggesting a different origin for the reported superconductivity.