Superconductivity at approximately 100 K in dense SiH4(H2)2 predicted by first principles.

Motivated by the potential high-temperature superconductivity in hydrogen-rich materials, the high-pressure structures of SiH(4)(H(2))(2) in the pressure range 50-300 GPa were extensively explored by using a genetic algorithm. An intriguing layered orthorhombic (Ccca) structure was revealed to be energetically stable above 248 GPa with the inclusion of zero-point energy. The Ccca structure is metallic and composed of hydrogen shared SiH(8) dodecahedra layers intercalated by orientationally ordered molecular H(2). Application of the Allen-Dynes modified McMillan equation yields remarkably high superconducting temperatures of 98-107 K at 250 GPa, among the highest values reported so far for phonon-mediated superconductors. Analysis reveals a unique superconducting mechanism that the direct interactions between H(2) and SiH(4) molecules at high pressure play the major role in the high superconductivity, while the contribution from H(2) vibrons is minor.