Theoretical investigations were made of chemical trends in the electronic properties of transition-metal impurity-pair complexes. Self-consistent spin-unrestricted electronic-state calculations were carried out, using a scalar relativistic scheme within the framework of the multiple-scattering molecular cluster method, for the substitutional Au 3d interstitial transition-metal pairs with C3v symmetry. The role which was played by the 5d and 3d states of transition metals in creating impurity energy levels in the crystal band-gap was established. Analysis of the 1-electron energy spectra of AusTii, AusVi, AusCri, AusMni, AusFei, AusCoi and AusNii pair impurities led to the conclusion that the electronic, magnetic and optical properties of the series could be explained by means of a simple microscopic model. This did not provide support for the ionic model, in which these pairs were described as being 2 point charges that were electrostatically bound by strong magnetic coupling between their spins. The results instead led to a model in which covalent effects were invoked in order to explain chemical trends, and the physical properties of the complexes.

Electronic properties and hyperfine parameters of gold 3d transition-metal impurity pairs in silicon L.V.C.Assali, J.F.Justo: Physical Review B, 1998, 58[7], 3870-8