Many-pole model of inelastic losses applied to calculations of XANES
Résumé
Conventional Kohn-Sham band-structure methods for calculating deep-core x-ray spectra
typically neglect photoelectron self-energy effects, which give rise to an energy-dependent shift and
broadening of the spectra. Here an a posteriori procedure is introduced to correct for these effects. The
method is based on ab initio calculations of the GWself-energy using a many-pole model and a calculation
of the dielectric function in the long wavelength limit using either the FEFF8 real-space Green’s function
code, or the AI2NBSE interface between the National Institute of Standards and Technology (NIST) Bethe-
Salpeter equation solver (NBSE) and the ABINIT pseudopotential code. As an example the method
is applied to core level x-ray spectra of LiF and MgAl2O4 calculated using (respectively) OCEAN, an
extension of the AI2NBSE code for core level excitations, and the PARATEC pseudopotential code with the
core-hole treated using a super-cell. The method satisfactorily explains the discrepancy between experiment
and calculations.