Tight-binding theory of manganese and iron oxides

Abstract

The electronic structure is found to be understandable in terms of the free-atom term values and universal interorbital coupling parameters, since self-consistent tight-binding calculations indicate that the Coulomb shifts of the $d$-state energies are small. The special-points averages over the bands are seen to be equivalent to the treatment of local octahedral clusters, so that all properties are given by algebraic formulas in terms of these parameters. The cohesive energy per manganese for MnO, ${\text{Mn}}_{2}{\text{O}}_{3}$, and ${\text{MnO}}_{2}$, in which manganese exists in the valence states ${\text{Mn}}^{2+}$, ${\text{Mn}}^{3+}$, and ${\text{Mn}}^{4+}$, is very nearly the same and dominated by the transfer of manganese $s$ electrons to the oxygen $p$ states. There are small corrections, 1.37 eV per Mn in all cases, from the couplings of the minority-spin states. Transferring one majority-spin electron from an upper cluster state to a nonbonding oxygen state adds 1.67 eV to the cohesion for ${\text{Mn}}_{2}{\text{O}}_{3}$ and the two transfers add twice that for ${\text{MnO}}_{2}$. The electronic and magnetic properties are consistent with this description and appear to be understandable in terms of the same parameters.