Many-Pole Self-Energy Model Corrections to Kohn-Sham Calculations of Excited State Spectra*

Experimental x-ray spectra are systematically shifted and broadened with respect to conventional density functional theory calculations due to photoelectron self-energy effects. We have recently developed an efficient many-pole model of the GW self-energy based calculations of dielectric responce using a real-space Green's function approach.\footnote{J.J. Kas et al., Phys. Rev. B {\bf 76}, 195116 (2007).} The model is applied \textit{a posteriori} to Kohn-Sham calculations of excited state spectra using a convolution of the spectrum with an energy dependent Lorenzian. The method is found to be widely applicable over a broad range of energies, with little computational cost. Several illustrative examples are presented which show improved agreement between theoretical calculations and experiment for both optical and x-ray spectra.