Establishment of the ab initio method for excited states and analysis of the anomalous X ray scattering spectra

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1. We have calculated the resonant x-ray scattering spectra near the vanadium K-edge in YVO_3 using an ab initio band calculation. Against a usually adopted interpretation that the intensity on the orbital ordering superlattice spot is a direct reflection of the ordering, we have found that the intensity comes from the lattice distortion, the Jahn-Teller type and the GdFeO_3 type. This is due to the extended nature of the 4p states of vanadium. Each type is found to play a different role on the spectral shape, in good agreement with the recent experiment.2. We have analyzed the resonant x-ray scattering spectra near Ce L_<III>-edge in the quadrupolar ordering phase of CeB_6 on the basis of a tight-binding model. Different from the case of transition-metal oxides, the intensity on the quadrupolar ordering superlattice spot is found to come from the 5d states modulated by the anisotropy of the charge distribution associated with the direction of the quadrupole moment through the 5d-4f Coulomb interaction.3. We have calculated the resonant magnetic x-ray scattering spectra near Ni K-edge in NiO, using a tight-binding model. It is found that the main peak due to the dipole transition arises from the 4p states orbitally polarized by the orbital moment at neighboring sites, and that the pre-edge peak due to the quadrupole transition arises directly from the 3d states having the orbital moment, in good agreement with the recent experiment.