Influence of hydrogen absorption on low-energy electronic collective excitations in palladium

A theoretical study of electronic excitation spectra in Pd and PdH is reported. The calculations were performed with full inclusion of the electron band structure obtained within self-consistent pseudopotential approach. We demonstrate that the complicated Pd electronic structure at the Fermi level is reflected in a numerous peak structure of the excitation spectra. The evolution of the energy-loss spectrum with momentum and its anisotropy are analyzed. Strong modification of the excitation spectra upon hydrogen absorption is found. We also study the role of intra- and interband transitions in the formation of dominating plasmon peak both in pure Pd and PdH. In Pd, this peak is mainly determined by intraband transitions. The downward shift of this peak from similar to 7.2 eV in pure Pd to similar to 4.2 eV in PdH is mainly explained by interband transitions from occupied Pd d bands to unoccupied hydrogen-modified sp states in the 7-13 eV energy range.