Calculation and interpretation of K -shell x-ray absorption near-edge structure of transition metal oxides

Simultaneous calculations of both K-edge x-ray-absorption near-edge structure (XANES) and ground-state electronic structure of $3d$ transition-metal oxides are presented. The calculations are based on a self-consistent one-electron real-space Green's-function approach, with many-body effects incorporated in terms of final-state potentials and a complex energy-dependent self-energy. The results are found to be in semiquantitative agreement with experiment at the metal K edges, except at the edge itself where a leading edge peak is found to be systematically low in intensity. A scattering theoretic interpretation is presented, which correlates the structure in the XANES with projected electronic density of states. This interpretation illustrates the crossover from a molecular orbital to a continuum resonance description of excited states. The importance of the core-hole potential in these calculations is also discussed.