First-principles study of rare-earth oxides

The self-interaction-corrected local-spin-density (SIC-LSD) approximation is used to describe the electronic structure of dioxides REO2 and sesquioxides RE2O3 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 ground-state configuration is found to be the most favorable. 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 CeO2, PrO2, and TbO2 exist in nature. Tetravalent NdO2 is predicted to exist as a metastable phase-unstable toward the formation of hexagonal Nd2O3.