Density-functional study of perovskite-type hydride LiNiH₃ and its synthesis: Mechanism for formation of metallic perovskite

A metallic perovskite-type hydride LiNiH₃ was synthesized based on first-principles prediction. We theoretically examined its electronic structure and found that half of the Ni-H derived antibonding states are occupied and that the modest thermodynamic stability depends on a delicate balance between (i) destabilization and (ii) alleviation of compression frustration in corner-sharing octahedra, both of which arise from occupation of antibonding states. Through density-functional analyses of the electronic structure and lattice instability extending over LiTH₃ series (T = Fe, Co, Ni, and Cu), we showed that the balance is in fact reflected in their thermodynamic stability.