[Wien] The calculation principles of X-ray absorption spectra by wien2k

Dear all, First I would like to express my thanks to Dr. Mukesh Sharma for sending me the references. I read through these two reference and they turn out to be on x-ray emission spectra. I wonder whether there are references about the principles (formulas and derivations) for x-ray absorption s

[Wien] The calculation principles of X-ray absorption spectra by wien2k

Dear all, I know that the x-ray absorption spectra are calculated for the dipole allowed transitions, generating matrix elements, which are multipliedwith a radial transition probability and the partial densities of states as explained in the userguide. But I want to know more detailed principl