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O: Fachverband Oberflächenphysik

O 46: Density functional theory and beyond for real materials I

O 46.6: Vortrag

Mittwoch, 24. März 2010, 11:45–12:00, H34

The calculations of the XANES L edges 3d compounds — •Robert Laskowski and Peter Blaha — Vienna University of Technology, Institute of Materials Chemistry, Vienna, Austria

We report on the calculations of the x-ray absorption near-edge structure spectra focusing on the transition metals L edges. In our approach we solve Bethe-Salpeter equation (BSE) formulated in a basis of single particle states calculated within DFT. The presented method goes beyond the commonly used DFT electron-hole calculations and is an alternative to a relativistic Hartree-Fock configuration interaction method. The DFT core-hole method, cannot reproduce some features of the L edge spectra, usually interpreted as multiplet effects. For example in the single particle approximation, the branching ratio should be proportional to the occupancy of the corresponding core levels, for p3/2 and p1/2 branches it should be close to 2:1. However the measured branching ratio may be quite different, for example for 3d0 cations like K+, Ca 2+, Ti 4+ the p1/2 branch is enhanced such that a ratio closer to 1:1 is observed. We show that this is related to the interaction between elementary excitations from p3/2 and p1/2 core states in the BSE approach. Independent calculations performed for p3/2 and p1/2 branches result in a ratio close to 2:1 and only when the interaction between the p3/2 and p1/2 excitation is included the correct ratio is obtained.