New developments in the theory of X-ray absorption and core photoemission

There has been dramatic progress over the past decade both in theory and in ab initio calculations of X-ray absorption spectra (XAS) and core level X- ray photoemission spectroscopy (XPS). The theory of X-ray absorption fine s tructure (XAFS) is now reasonably well understood, and rapid progress is no w being made in understanding X-ray absorption near-edge structure (XANES). This talk reviews the developments in this field by many groups leading up to the current state. These developments have led to several ab initio cod es which permit a quantitative interpretation of the spectra in terms of ge ometrical and electronic properties of a material. High-order multiple scat tering (MS) theory can give an approximate treatment of XANES, but this app roach can fail close to an edge, where full MS calculations are often neces sary. Nevertheless a fully quantitative treatment of XANES remains challeng ing, due to a number of many-body effects, e.g. the approximate treatment o f the core-hole, multiplet effects, the photoelectron self energy, and inel astic losses. Essentially the same underlying theory has been applied to a number of other spectroscopies such as XPS, anomalous X-ray scattering (AXS ), DAFS (diffraction anomalous fine structure) and XMCD (X-ray magnetic cir cular dichroism). These developments are illustrated with a number of appli cations. (C) 2001 Elsevier Science B.V. All rights reserved.