Ab-initio study of pressure dependent physical properties and possible high-Tc superconductivity in monoclinic and orthorhombic MgVH6

In this work, we have used the density functional theory (DFT) to investigate the structural, mechanical, electronic, thermal, superconducting transition temperature (Tc) and optoelectronic properties of predicted monoclinic (P21/m) and orthorhombic (Pmn21) structures of MgVH6 at different pressures. Considering phase stability, we have studied optical properties for the monoclinic structure at 0 GPa and the orthorhombic structure at 100 GPa only. It has been found that both the structures of MgVH6 are chemically stable in the pressure range considered. On the other hand, the monoclinic structure is mechanically stable but the orthorhombic structure is mechanically unstable under the pressures considered. Monoclinic (P21/m) exhibits ductility in the pressure range 0 GPa-15 GPa. Orthorhombic (Pmn21) is brittle in nature at 100 GPa but shows ductility for pressures in the range from 125 GPa to 200 GPa. Hardness calculations indicate superhard character of orthorhombic (Pmn21) structure at 100 GPa. The melting temperature of orthorhombic crystal is very high. This finding also agrees with the bulk modulus, Debye temperature, and hardness calculations. Furthermore, we have calculated theoretically the superconducting transition temperature (Tc) at different pressures only for the orthorhombic (Pmn21) structure following a previous study. The estimated values of transition temperatures are within 88.55 K-22.11 K in the pressure range from 100 GPa to 200 GPa. The compound MgVH6, in both the structures, is elastically and optically anisotropic.