Theory of X-Ray Absorption

Abstract

This contribution concerns the interpretation of x-ray absorption spectra for the determination of the electronic structure. This subject has gained much impetus in recent years as a direct consequence of the experimental progress in the field of soft x-ray monochromators, like the SX700 plane-grating-monochromators [1] and the DRAGON mono chromat or, based on a cylindrical-grating [2]; both monochromators reaching up to 1:10.000 resolution in the soft x-ray range. This stimulated the development of many new fields one of which is 2p x-ray absorption (L 2,3-edges) of the 3d transition-metal compounds. The high resolution, combined with the relative long lifetime of the excited states, result in extremely sharp spectra with complex shapes. In the process of explaining these shapes it was immediately clear that the role of the core-hole was of central importance, like in the case of 3d x-ray absorption spectra (or M 4,5-edges) of the Rare-Earths. The experiments on the M 4,5-edges in the sixties [3] were, for some early Rare-Earths, partially explained with an atomic multiplet approach, developed in the early seventies [4]. This approach was improved and generalized to all Rare-Earths by Thole et al. and good agreement was found with experiment [5]. Although the atomic multiplet results show some likeness with the L 2,3-edges of the 3d transition-metal compounds, solid state effects modify the spectra to such extend that detailed analysis calls for a change in the approach. In the following we will in short give an overview of the some models to simulate the x-ray absorption cross section.KeywordsCrystal FieldCore HoleMultipole InteractionDensity Functional ApproachCrystal Field StrengthThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.