Calculation of LII, III X-ray absorption spectra for 3d transition metals

Professor P. Blaha (Technische Universität Wien, Austria) and his colleagues have recently calculated the X-ray absorption spectra at the L_{II, III} edges of the early 3d elements by solving the Bethe-Salpeter equation (BSE). Under the independent particle approximation (IPA), X-ray absorption spectra are usually considered as proportional to the unoccupied part of the projected density of states weighted by the momentum matrix elements between the core and the conduction states. However, due to the localization of the core wave function, the interaction of the exited electron with its hole is not negligible. In particular, the branching ratio between the L_II and L_III edges cannot be explained. Though the IPA gives 1:2, the observed ratios are much closer to 1:1 or even higher for K, Ca, Sc, Ti, and V. They detailed this problem based on their BSE calculation. For more information, see the paper, "Understanding the L2,3 x-ray absorption spectra of early 3d transition elements", R. Laskowski et al., Phys. Rev. B 82, 205104 (2010).