Theory of many-body effects in valence, core-level and isochromat spectroscopies along the 3d transition metal series of oxides

Core level X-ray photoemission and absorption spectra (XPS and XAS) are calculated for some transition metal (TM) insulating compounds, especially oxides, using a configuration-interaction impurity-Anderson model combined with the influences of the core effect. Our model calculation is able to explain well the core-XPS of a series of early TM compounds, characterized by a nominally 3d⁰ configuration in the ground state, including those compounds which involve pre-transitional elements such as potassium or calcium. The standard "linear muffin-tin orbital" (LMTO) band structure for TiO₂ compounds in rutile structure is recalled and compared to experimental valence photoemission spectra. A few characteristics of the outcoming density of states (DOS) are used to interpret the Ti2p XPS in the simplest way within the previously considered Anderson model; however, for the onset of the Ti K-edge XAS, the calculated DOS of TiO₂ does not predict the very first weak peak, indicating that this feature is not simply due to a one-electron (dipole) transition and needs to be interpreted by taking into account both dipole and quadrupole transitions; moreover it is necessary to take into account an additional phenomenon, i.e. the 1s core hole effect, which is characteristic of the Ti K-edge and of course absent from the Bremsstrahlung isochromat spectroscopy (BIS) as is shown from a comparative study between XAS and BIS. For the interpretation of the core level spectra, the considered early TM oxides (TiO₂ for example) resemble the late TM oxides, such as MnO,..., CuO, and belong to the charge transfer regime; in the case of CuO, in order to explain the 2p XPS satisfactorily, the full multiplet coupling between a Cu3d hole and a Cu2p core hole is taken into account together with the corresponding spin-orbital interactions at the expense of considering only the cluster version of the Anderson model.