Ab initio Calculations of X-ray Spectra: Comparison with Accurate Measurements

A number of advances in the theory of x-ray absorption (XAS) have been developed with the aim of achieving a parameter-free treatment of the key many-body effects.\footnote{J. J. Rehr et al., Comptes Rendus Physique, {\bf 10}, 548 (2009)} These include a GW many-pole self-energy model, {\it ab initio} Debye-Waller factors, and an RPA screened core-hole. These developments have been implemented in the real-space multiple-scattering code FEFF9.0, and applied to calculations of x-ray absorption spectra and electron energy loss spectra as well as a variety of other core level spectroscopies. Calculations span a broad spectrum from the visible to x-ray energies. Results for a number of materials are compared with previous theories and with accurate experimental data.