Ab initio prediction of superconductivity in molecular metallic hydrogen under high pressure

We present a first ab initio investigation of the electron–phonon coupling (EPC) of molecular metallic hydrogen with a Cmca structure based on the linear-response approach. This molecular metallic hydrogen with overlapping bands has an elastic instability at lower pressures (<300 GPa), but stabilizes dynamically under further compression as indicated by the absence of phonon softening, thus supporting the choice of Cmca structure as a good candidate for metallic hydrogen. Within the conventional BCS theory, the predicted critical temperature T c is 107 K at 347 GPa, so indicating good candidacy for a high temperature superconductor. With increasing pressure, interestingly, the EPC parameter λ , hence, T c increases, resulting from the increased electronic density of states at the Fermi level and EPC matrix element 〈 I 2 〉 , in spite of an enhanced average phonon frequency 〈 ω 2 〉 .