Investigation of stable germane structures under high-pressure.

The evolutionary structure-searching method discovers that the energetically preferred compounds of germane can be synthesized at a pressure of 190 GPa. New structures with the space groups Ama2 and C2/c proposed here contain semimolecular H2 and V-type H3 units, respectively. Electronic structure analysis shows the metallic character and charge transfer from Ge to H. The conductivity of the two structures originates from the electrons around the hydrogen atoms. Further electron-phonon coupling calculations predict that the two phases are superconductors with a high Tc of 47-57 K for Ama2 at 250 GPa and 70-84 K for C2/c at 500 GPa from quasi-harmonic approximation calculations, which may be higher than under actual conditions.