First-principles total energy calculations were performed for aggregate defects of Pt or Au with Li. The calculations were carried out within the local spin density approximation of density functional theory, using the linear muffin-tin orbital method in the atomic spheres approximation. Estimates were made of the binding energies of the aggregates (ignoring lattice relaxations), and of the hyperfine interactions. It was shown that, in the case of the aggregate defects which were observed experimentally, the noble metal atom was always on a lattice site. There was a stable orthorhombic pair that consisted of one Li atom on an interstitial site close to the noble metal impurity, and a trigonal aggregate that consisted of the noble metal; surrounded by three Li atoms on the nearest interstitial sites. Hyperfine interactions with the noble metal, with Li, and also with Si, were explained quantitatively by using an extension of the vacancy model. It was shown that the 29Si nucleus which gave rise to the prominent hyperfine interaction was on a normal lattice site. Aggregates that involved two Li atoms were not stable, but there was a stable aggregate in which four Li atoms were situated around one Pt atom in a tetrahedral configuration. The analogous aggregate with Au had no state in the gap, and was therefore expected to be a stable end product of the gettering of Au by Li. On the other hand, its presence was likely to be difficult to prove experimentally.

H.Weihrich, H.Overhof, P.Alteheld, S.Greulich-Weber, J.M.Spaeth: Physical Review B, 1995, 52[7], 5007-20