Electronic structure and hyperfine interactions in the FeO42−ion

Self-consistent-field $X\alpha$-scattered-wave calculations were performed for the ferrate ion (Fe${\mathrm{O}}_4^{2-}$) in spin-restricted and spin-unrestricted schemes. Valence ionization energies are obtained and compared to experimental values. The charge and spin densities at the Fe nucleus derived from these calculations are related to Mössbauer-isomer-shift and hyperfine-field values. Results show that the occupation of the $3d$ orbital is much higher than in the formal $3d^2$ configuration, but the effective number of unpaired electrons is less than two.