Ab initio analysis of electron energy loss spectra for complex oxides

The local electronic structures in ionic materials are analysed in terms of the site- and angular-momentum-projected densities of states, which are obtained from self-consistent ab initio band-structure calculations. The unoccupied conduction-band states are compared to the energy-loss near-edge spectra (ELNES), which are measured by analytical transmission electron microscopy with high spatial resolution. A novel tool for the interpretation of this ELNES data is presented: The projection of the calculated density of states onto an optimised atomic-orbital basis set allows a neighbourhood-sensitive electron-distribution analysis based on crystal orbital overlap populations. This method is applied to spinel, MgAl2O4, both in its regular and in its inverse structure. An analysis of the O–K-edge gives evidence of a distinction between the influences of tetrahedrally coordinated and octahedrally coordinated cations on the near-edge structure.