First-principles investigations of transition metal dihydrides, TH₂: T = Sc, Ti, V, Y, Zr, Nb; energetics and chemical bonding

Self-consistent full-potential linearized augmented-plane-wave (LAPW) band-structure calculations are performed for the fluorite-type dihydrides ScH2, TiH2, VH2, YH2, ZrH2 and NbH2 as well as for the tetragonal low-temperature phases of TiH2 and ZrH2. For all compounds studied which show metallic behaviour, band structures, densities of states, electron densities and the total-energy minima with respect to the lattice parameters are computed. Additionally, the bulk moduli for the cubic phases are given. Good agreement with experimental data is found where they are available. The results obtained confirm previous interpretations of the tetragonal distortion of the cubic unit cell as a Jahn-Teller-type effect and show how the electron densities of the tetragonally distorted phases depend on the splitting of states near the Fermi level. The total-energy curves for TiH2 and ZrH2 as functions of the c/a ratios show two minima each, of which only the ones for c/a<1 have been observed experimentally.