Electronic States of Fe in I–III–VI₂ Compounds

Abstract

The electronic states of a tetrahedral cluster of a Fe ion and four S ions are calculated in order to obtain the electronic structure around a Fe ion in I–III–VI₂ compounds. The LCAO-MO scheme is used with account of configuration interactions (CI). The ground state is found to have ⁶A₁ symmetry and two ⁶T₂ states, to which allowed transitions are expected, are obtained in an energy region below the fundamental absorption edge, in agreement with experiments. It is remarked that the ground ⁶A₁ state arises by no means from the pure atomic d⁵ configuration: mixing of charge transferred configurations is quite large. The energies of quartet states (⁴T₁, ⁴T₂) are lower than those of the corresponding sextet states (⁶T₁, ⁶T₂) in harmony with the observed optical spectra. Account of CI is essential to the findings.