Inert Gases in Solids: Interatomic Potentials and Their Influence on Rare-Gas Mobility

Abstract

A modification of the Wedepohl method for the determination of interatomic potentials between closed-shell atoms and ions was developed and applied to the rare gases. Both Slater and Kohn-Sham exchange approximations were employed in the calculation of the atomic charge distributions and also in the overlap region between the atoms. The He-${\mathrm{Cu}}^{+}$ and short-range ${\mathrm{Cu}}^{+}$-${\mathrm{Cu}}^{+}$ interactions were calculated by the same technique. Using five different potentials to describe the copper lattice, the minimum energy configuration of an interstitial He atom was determined. The (1, 0, 0) octahedral position in the lattice was found to be most stable, independent of the potential. Despite the variations in the potentials, the activation energy for He migration was found to lie within the narrow range 0.45 to 0.71 eV and the path of migration was found to be along a crystallographic direction. Our calculations therefore show that interstitial He atoms will be mobile at or below room temperature in a trap-free copper lattice.