Pressure-Driven Structural Phase Transitions and Superconductivity of Ternary Hydride MgVH6

A systematic investigation of ternary hydride MgVH6 within the pressure range of 0-200 GPa has been performed by means of the particle swarm optimization algorithm and density functional theory. Results of an extensive structure search and full relaxation further indicate that three new phases, P2(1)/m, C2/m, and Pmn2(1), appear successively with the increasing of pressure, which contain two first-order structural phase transitions from P2(1)/m to C2/m about 32 GPa and from C2/m to Pmn2(1) about 93 GPa. Three phases are all metallic phases by analyzing their band structures and density of electronic states and are also dynamically and mechanically stable based on their phonon spectra and elastic properties. More importantly, the electron-phonon coupling calculation indicates that MgVH6 with Pmn2(1) symmetry is a promising superconductor with an estimated superconducting transition temperature of 27.6 K at 150 GPa, which is similar to the superconducting transition temperature of 35 K at 300 GPa of ternary hydride LaSH 6 (Phys. Rev. B 2019, 100, 184502). Further analysis of the electron- phonon coupling mechanism shows that the superconductivity is mainly derived from the strong electron-phonon interaction of heavier transition metal V atoms.