First-principles study on crystal structures and superconductivity of molybdenum hydrides under high pressure

Abstract

Hydrogen-rich compounds are promising candidates for high temperature superconductors [Duan et al., Natl. Sci. Rev. 4, 121 (2017); Bi et al., arXiv:1806.00163 (2018); Pickard et al., Ann. Rev. Condens. Matter Phys. 11, 57 (2020); Flores-Livas et al., Phys. Rep. 856, 1 (2020)]. Combining first-principles calculation and the swarm intelligence-based structure search method, we investigated structures and superconductivity of molybdenum hydrides under high pressures. Four new phases have been predicted, namely, I4/m−MoH4, I4/mmm−MoH4, C2/m−MoH6, and Immm−MoH6. The superconducting critical temperature of Immm−MoH6 under 300 GPa was predicted to be 80 K, which is the highest value among hydrides of group six elements in the periodic table. Intriguingly, the phase transition from I4/mmm−MoH4 to I4/m−MoH4 at 280 GPa is driven by the imaginary optical modes and the soft optical modes significantly enhance the superconducting critical temperature.