Electronic structure calculations for LaNi5 and LaNi5H7:: energetics and elastic properties

Density functional calculations of the electronic structure and enthalpy of formation DeltaH of LaNi5 and LaNi5H7 are reported. Single-crystal elastic constants and Voigt-Reuss-Hill polycrystalline moduli were calculated for both materials using a stress-based least-squares fitting methodology. We obtain DeltaH(0K) = -40 kJ/mol H-2 for the hydride at zero temperature. Incorporating a Debye estimate of the phonon contribution we find DeltaH(298 K)similar to-39 kJ/mol/H-2, a value that compares favorably with experimental determinations of -32 to -35 kJ/mol/H-2. Our results indicate that the H-Ni and H-La interactions in the hydride are primarily metallic with a small ionic component. The calculated elastic moduli are in excellent accord with single-crystal measurements on LaNi5 and with available data for polycrystalline samples of the parent and hydride. (C) 2002 Elsevier Science B.V. All rights reserved.