Fully relativistic calculations of the L_2,3-edge XANES spectra for vanadium oxides

Fully relativistic multielectron method based on the numerical solution of the Dirac equation was used to calculate the L_2,3-edge X-ray absorption near edge structure (XANES) spectra of VO₂, V ₂O₃, and V₂O₅ crystals. The key-points of the method are: i) usage of the molecular orbitals (MO); ii) absence of any fitting parameters; iii) wide area of application: to any ion in any symmetry; iv) possibility of numerical analysis of the MO composition. The calculated spectra are in a satisfactory agreement with experimental data available in the literature, including the absolute values of the transitions energy, the shape of the absorption bands, and polarization dependence. The assignment of the absorption bands in terms of the electronic configurations was done. The structure of the absorption bands is attributed to the splitting of the vanadium p- and d-orbitals; the magnitude of this splitting is estimated from the spectra. Covalency effects were considered for all hosts; it was shown that the contribution of the oxygen wave functions increases with increasing the vanadium oxidation state. Dependence of the relative positions of the vanadium 3d and oxygen 2p levels and energies of the "ligand-metal" charge transfer transitions on the vanadium oxidation state was analysed.