Forces, Dipole Force Tensor and Elastic Binding Energy in α-Palladium Hydrides

Abstract

The forces resulting from the presence of one interstitial Hydrogen in Palladium are deduced from the variation of the total energy of the alloy up to first order in the atomic displacement. This variation includes the band term together with the electron-electron and ion — ion terms but, unfortunately, neglects the zero point motion of the Hydrogen. This tight-binding calculation is based on a rigidly moving wave function basis where the electronic structure of the unrelaxed alloy is determined by taking into account a perturbing potential up to the nearest neighbours of the Hydrogen atom. Expressions of the distribution of the forces and of the dipole force tensor P are derived in terms of the variation of the hopping integrals and of the energy levels. Estimations of P and of the forces up to third nearest neighbour shell of the Hydrogen atom are presented. Once this has been done the elastic binding energy can be obtained if we know the lattice Green function of the alloy. In the present model we replace this unknown exact Green function by a phenomenological expression of the host lattice Green function.