Electronic response of hydrogen storage intermetallics LaNi5 and LaNi4.5Co0.5: inelastic scattering experiment and ab initio calculations

Abstract

Electron momentum densities of intermetallic compounds LaNi5 and LaNi4.5Co0.5 using inelastic scattering of 662 keV γ-rays are presented. To check the usefulness of different exchange and correlation potentials for such type of hydrogen storage compounds, the resulting experimental Compton profiles (CPs) have been compared with the Compton lines deduced using linear combination of atomic orbitals (LCAO) scheme. It is seen that the LCAO with HISS scheme (middle range separated hybrid approach) leads to a better agreement with the experimental CPs than other considered schemes based on LDA, GGA, SOGGA, B3LYP and short range separated hybrid HSE06. In addition, energy bands and density of states of these systems derived using LCAO and the full potential linearized augmented plane wave methods are discussed. Anisotropies in momentum densities with respect to [001] direction namely (J001−J110 and J001–J100) show almost similar trend for both the intermetallics. It is noticed that the energy states corresponding to d states of Ni (2c), Ni (3 g) and Co atoms dominate near Fermi level (EF). The Fermi surface (FS) topology and real space CPs of LaNi5 and LaNi4.5Co0.5 show non-spherical character of FS and failure of free electron theory for such intermetallics.