Superconductivity determined by the S–H framework in CH4-inserted S–H framework hydrides under high pressures

Recently, a debate is raising the concern of possible carbonaceous sulfur hydrides with room-temperature superconductivity around 270 GPa. In order to systematically investigate the structural information and relevant natures of C–S–H superconductors, we performed an extremely extensive structure search and first-principles calculations under high pressures. As a result, the metastable stoichiometries of CSH7, C2SH14, CS2H10, and CS2H11 were unveiled under high pressure, which can be viewed as CH4 units inserted into the S–H framework. Given the super-high superconductivity of Im3̄m-SH3, we performed electron–phonon coupling calculations of these compounds,the metastable of R3m-CSH7, Cm-CSH7, Cm-CS2H10, P3m1-CS2H10, Cm-CS2H11, and Fmm2-CS2H11 are predicted to become good phonon-mediated superconductors that could reach Tc of 130, 120, 72, 74, 92, and 70 K at 270 GPa, respectively. Furthermore, we identified that high Tc is associated with the large contribution of the S–H framework to the electron density of states near the Fermi level. Our results highlight the importance of the S–H framework in superconductivity and verify that the suppression of density of states of these carbonaceous sulfur hydrides by CH4 units results in Tc lower than that of Im3̄m-SH3, which could act as a useful guidance in the design and optimization of high-Tc superconductors in these and related systems.