  The discovery of the high temperature superconducting state in compounds of
hydrogen, carbon and sulfur with the critical temperature (Tc) of 288 K at high
pressure is an important milestone towards room-temperature superconductors.
Here, we have extensively investigated the high-pressure phases of CS2H10, and
found four phases Cmc21, P3m1, P-3m1 and Pm. Among them, P3m1 can be
dynamically stable at pressure as low as 50 GPa, and Cmc21 has high Tc of 155 K
at 150 GPa. Both of Cmc21 and P3m1 are host-guest hydrides, in which CH4
molecules are inserted into Im-3m-H3S and R3m-H3S sublattices, respectively.
Their Tc is dominated by the H3S lattice inside. The insertion of CH4 greatly
reduces the pressure required for the stability of the original H3S lattice,
but it has a negative impact on superconductivity that cannot be ignored. By
studying the effect of CH4 insertion in the H3S lattice, we can design hydrides
with Tc close to that of H3S and a greatly reduced pressure required for
stability.
