Electronic configuration and electric field gradient in Au complexes

Abstract

Using the relativistic Hartree-Fock method and a renormalized-atom scheme, we have calculated $〈r^{-3\mathrm{}}〉$ values for the $6p$ and $5d$ orbitals of Au in several configurations. The object of renormalization is to deal with orbitals localized at the Au site rather than with functions extending well out into the surrounding lattice, as is the case when a free-atom Au-$6p$ function is used to represent the $6p$ orbital character in a crystal. We find that while ${〈r^{-3\mathrm{}}〉}_{5d}$ values are relatively insensitive to the renormalization, ${〈r^{-3\mathrm{}}〉}_{6p}$ values obtained from calculations renormalized to the Wigner-Seitz radius of Au are larger by factors of 2 to 4 than those from free-atom calculations. Renormalized ${〈r^{-3\mathrm{}}〉}_{6p}$ values, in contrast to those for the free atom, considerably exceed ${〈r^{-3\mathrm{}}〉}_{5d}$ values and are less sensitive to variation of electronic configuration. Using the renormalized ${〈r^{-3\mathrm{}}〉}_{6p}$, we have been able to interpret the large Mössbauser quadrupole splittings observed in covalent Au(I) compounds in terms of $\sigma$ bonding. Other implications from these results are discussed.