Combined Bethe-Saltpeter equations and time-dependent density-functional theory approach for x-ray absorption calculations

Many-body effects such as local fields and the core-hole interaction can be significant in x-ray absorption spectra even several hundred eV above an absorption edge. The treatment of these effects requires theories beyond the independent-particle approximation, e.g., the Bethe-Saltpeter equation (BSE) or the time-dependent density-functional theory (TDDFT). However the BSE is usually limited to low energies, while the TDDFT often ignores the nonlocality of the core-hole interaction. Here we present a combined approach for the calculations of the x-ray spectra that include both of these effects, together with inelastic losses and self-energy shifts over a wide energy range. The approach is illustrated for a few materials, including metals and oxides.