First-Principles Investigation of Metal-Hydrogen Interactions in NbH

First-principles total-energy calculations have been performed for NbH in the $\beta$- and $\gamma$- phase structures. Lattice constants, bulk moduli, and heats of formation as well as the frequencies and second harmonics of the optical vibrations of hydrogen and deuterium in the lattice have been calculated and found to be in excellent agreement with experiment. Our calculated electronic densities of states resolve the discrepancy between previous band calculations and photoemission experiments.