INTERACTION ENERGIES OF PERTURBED-ANGULAR-CORRELATION PROBES WITH IMPURITIES IN AG AND PD

We present systematic ab initio calculations of the nearest-neighbor interaction energies of perturbed-angular-correlation (PAC) probe atoms (Rh-99, Pd-100, In-111) with 4d and 5sp impurity atoms (Zr-Sb, with Z = 40-51) in Ag and Pd crystals. The calculations are based on local-density theory and apply the Korringa-Kohn-Rostoker Green's-function method for spherical potentials. The full nonspherical charge density is evaluated to calculate the double-counting contributions to the total energy. The present calculations reproduce very well most of the available experimental interaction energies of probe-impurity pairs in the two metal hosts. It is shown that the interactions of the 4d-4d probe-impurity pairs in Ag and Pd can be understood by considering both the changes of the d bond and the repulsive energies between the different atomic rearrangement of isolated probe and impurity atoms and of the probe-impurity pair. On the other hand, the interactions of the 5sp-5sp probe-impurity pairs as well as 4d-5sp and 5sp-4d in Ag can be explained by a change in the electrostatic interaction induced by the changes of the nuclear charges of the probe and impurity atoms with respect to the host atom. It is found that the calculated interaction energies of the Ag 100PdX and (RhX)-Rh-99 (X = Zr-Sb) systems, where the probe atoms are neighboring elements of the host atoms, can very well be reproduced by the Miedema-Krolas model. Some comments are also made on the experimentally obtained attraction for the Pd (RhX)-Rh-99 (X = Cd-Sb) systems, which cannot be reproduced by present calculations.