Correlation between the Electrostatic Potential and the Occupation of Interstitial Sites by Hydrogen in Metallic Systems

The electrostatic crystal potentials V(r) of the cubic metals Pd, V, Nb, Ta, and the intermetallic phases FeTi and XEr, X = Cu, Ag, Au, have been determined by the full potential augmented-plane-wave method (FP-APW). Furthermore, to study the electronic states in dilute metal-hydrogen-systems the partial densities of states have been calculated by the supercell procedure using the augmented-spherical-wave method (ASW) for PdH_1/32. The results are compared with the values for PdH_1/4, PdH, and Pd. – A relation is found between the depth of the host lattice electrostatic potential and the occupation of interstitial lattice sites by hydrogen in the metal-hydrogen α-phases. For bcc V, Nb, and Ta the crystal potential “seen” by a proton has its deepest minimum at the tetrahedral site, for fcc Pd the minimum occurs at the octahedral site and in FeTi (B2-type) the minimum of V_proton(r) is found for the octahedral site surrounded by 2 Fe atoms and 4 Ti atoms. In all these cases the calculated site of the minimum is in accordance with the location of hydrogen in the respective α-phases found experimentally by neutron scattering. For XEr. X = Cu, Ag, Au, a preferred occupation by hydrogen is predicted.