Abstract
The electronic structures of Fe3+ coordination sites in hematite and maghemite are obtained from self-consistent field Xα scattered-wave (SCF-Xα-SW) molecular orbital calculations on an octahedral (FeO6)9− cluster, a trigonally distorted (FeO6)9− cluster, and a tetrahedral (FeO4)5− cluster. The electronic structures of these coordination sites should also give a good description of those of Fe3+ cations in other oxides and silicates. The overlapping sphere approach to the SCF-Xα-SW formalism is used and is found to give more accurate results than previous calculations on these systems.
Multiplet theory is used to relate the one-electron molecular orbital energies to the ligand field spectra of Fe3+ in oxides. Calculated energies of ligand to metal charge transfer transitions agree with experimental data and are used to interpret the near-UV spectra of Fe3+ oxides and silicates.
The calculated wavefunctions show that chemical bonds in Fe3+ oxides are fairly covalent. Moreover, the Fe-O bond has a strong spin polarization. The spin dependance of the covalency explains how superexchange and the main features of the magnetic structures of iron oxides are predicted from simple (FeO6)9− and (FeO4)5− cluster calculations.
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Sherman, D.M. The electronic structures of Fe3+ coordination sites in iron oxides: Applications to spectra, bonding, and magnetism. Phys Chem Minerals 12, 161–175 (1985). https://doi.org/10.1007/BF00308210
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DOI: https://doi.org/10.1007/BF00308210