Model calculation of core level XPS spectra in early 3d-metal compounds

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Abstract
Using a configuration-interaction impurity-Anderson model we calculate core-hole X-ray Photoemission Spectra (c-XPS) for some early Transition Metal (TM) insulating compounds. Because in these compounds the valence (ligand) band is completely filled, the TM on-site Coulomb repulsion Udd is treated exactly, as well as the 3d-core hole interaction Udc. The ground state of such a ligand-TM system with a nominally d0 cation is described as a mixture of purely d0 ionic state, and charge-transfer screened d1L and d2L2 states where L denotes a hole in the ligand band. Our simplified model enables us to understand why c-XPS satellites are still present in CaF2 or CaO, like in light TM compounds, but absent for KF compounds. In addition to Udd and Udc, the other relevant parameters are the ligand-to-metal charge-transfer energy Δ and the corresponding hybridization V (related to the metal-ligand transfer integrals). Finally quite a good fit to 2p3/2-XPS of TiO2 is obtained by using the parameter values estimated from (i) a LMTO band structure calculation of TiO2, and (ii) another calculated fit of the K(Ti) pre-edge absorption spectrum in TiO2

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