Structural evolution and molecular dissociation of H₂S under high pressures

Solid H_2S as the precursor for H_3S with incredible superconducting properties under high pressure, has recently attracted extensive attention. Here in this work, we propose two new phases of H_2S with P4_2/n and I4_1/a lattice symmetries in a pressure range of 0 GPa-30 GPa through first-principles structural searches, which complement the phase transition sequence. Further an ab initio molecular dynamics simulation confirms that the molecular phase P2/c of H_2S is gradually dissociated with the pressure increasing and reconstructs into a new P2_1/m structure at 160 GPa, exhibiting the superconductivity with T_\rm c of 82.5 K. Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H_2S.