Crystal structures and superconductivity of carbonaceous sulfur hydrides at pressures up to 300 GPa

To explore the crystal structure of the recently claimed room-temperature superconducting carbonaceous sulfur hydrides, we searched for ???250 000 structures over ???800 stoichiometries at 300 GPa via advanced crystal structure searching and cluster expansion method. Only several metastable high-temperature superconductors were identified, whose structures can be classified into hydrogen-rich molecular crystals and low-level carbon-doped H3S-like structures by constructing the ternary phase diagram and simulating the electron-phonon interactions. The C???S???H molecular crystals are composed of CH4, SH6, and H2 molecules, where the superconductivity (with the highest superconducting critical temperature Tc is 156 K found in CSH48 at 300 GPa) is mainly contributed to by H2 units, implying their Tc values are unlikely to be higher than that of metallic molecular hydrogen (Tc of 242 K at 450 GPa). The highest Tc of low-level carbon-doped C???S???H compounds (up to 64 atoms in the primitive cell) at 300 GPa was estimated as 189 K for H3S0.917C0.083. Our results provide a comprehensive map between the crystal structure and superconductivity of carbonaceous sulfur hydride materials at high pressures.