Charge transfer excitation in resonant X-ray emission spectroscopy of NiO

We analyze Ni 2p -> 3d -> 2p resonant X-ray emission spectroscopy (RXES) of NiO with the impurity Anderson model. We pay attention to the inelastic X-ray scattering structures arising from the interatomic charge transfer (CT) from ligand state to 3d state. We take into account a finite width of the O 2p valence band in order to reproduce the experimental CT excitations in RXES, where two different CT structures are observed depending on the incident photon energy set in the CT satellite region of Xray absorption spectra. The origin of these two CT excitation peaks is ascribed to the lower and upper edges of the 3d(9)(L) under bar nonbonding band in the final state of RXES. The value of CT energy Delta is estimated from our calculation. By analyzing XAS and RXES simultaneously with changing Delta from 2.0eV to 6.5 eV by the step of 0.5 eV, we conclude that the most appropriate value of Delta is 3.5 eV. Also, in our calculation two different geometrical configurations are considered, which are called polarized and depolarized configurations (the polarization vector of incident photon is perpendicular and parallel to the scattering plane, respectively), although only the depolarized configuration is taken in the RXES experiments so far made. Our result predicts larger intensity of RXES near the elastic scattering in the polarized configuration.