Transition-metal hydrides: Electronic structure and the heats of formation

Calculations of the electronic structure of transition-metal hydrides are applied to the cohesive energy of $3d$ and $4d$ monohydrides, and the single-particle lifetime of states in nonstoichiometric Cu and Pd hydrides. A simple formula is presented which delineates the principal contributions to the cohesive energy of the hydrides: (i) the formation of a metal-hydrogen bonding level derived of states of the pure metal band structure which have $s$ symmetry about the site of the added proton, (ii) a slight increase in binding of the metal $d$ bands due to the added attractive potential, and (iii) the addition of an extra electron to the metal electron sea. The calculations, corrected for Coulomb repulsion at the hydrogen sites, qualitatively reproduce the experimental trends of the heats of formation of the transition-metal hydrides. The single-particle lifetime calculations are in quantitative agreement with Dingle-temperature measurements and they correctly predict the existence of essentially undamped states on the hole sheets of the $\ensuremath{\alpha}$-phase PdH Fermi surface.