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

1. 我们用从头算方法计算了YVO_3中钒k边附近的谐振x射线散射谱。与通常认为轨道有序超晶格点上的强度是有序的直接反映的解释不同，我们发现强度来自晶格畸变、Jahn-Teller型和GdFeO_3型。这是由于钒的4p态的扩展性质。发现每种类型对光谱形状起不同的作用，这与最近的实验很好地一致。基于紧密结合模型，分析了CeB_6四极有序相Ce L_<III>-边缘附近的共振x射线散射光谱。与过渡金属氧化物不同的是，四极有序超晶格点上的强度来自于通过5d-4f库仑相互作用与四极矩方向相关的电荷分布的各向异性调制的5d态。我们用紧密结合模型计算了NiO中Ni k边附近的共振磁x射线散射谱。偶极跃迁的主峰产生于被相邻位置的轨道矩极化的4p态，而四极跃迁的前边峰直接产生于有轨道矩的3d态，这与最近的实验结果吻合得很好。

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.