The self-interaction-corrected local-spin-density approximation is used to describe the electronic structure of dioxides, REO 2 , and sesquioxides, RE 2 O 3 , for the rare earths, RE=Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy and Ho. The valencies of the rare earth ions are determined from total energy minimization. We find Ce, Pr, Tb in their dioxides to have the tetravalent configuration, while for all the sesquioxides the trivalent groundstate configuration is found to be the most favourable. The calculated lattice constants for these valency configurations are in good agreement with experiment.Total energy considerations are exploited to show the link between oxidation and f -electron delocalization, and explain why, among the dioxides, only the CeO 2 , PrO 2 , and TbO 2 exist in nature.Tetravalent NdO 2 is predicted to exist as a metastable phase -unstable towards the formation of hexagonal Nd 2 O 3 .
We apply the self-interaction corrected local spin density approximation to study the electronic structure and magnetic properties of the spinel ferrites MnFe2O4, Fe3O4, CoFe2O4, and NiFe2O4. We concentrate on establishing the nominal valence of the transition metal elements and the ground state structure, based on the study of various valence scenarios for both the inverse and normal spinel structures for all the systems. For both structures we find all the studied compounds to be insulating, but with smaller gaps in the normal spinel scenario. On the contrary, the calculated spin magnetic moments and the exchange splitting of the conduction bands are seen to increase dramatically when moving from the inverse spinel structure to the normal spinel kind. We find substantial orbital moments for NiFe2O4 and CoFe2O4.
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