First principles calculations of optical and x-ray spectra from atomic coordinates alone

Theoretical calculations of various x-ray and optical spectroscopies often rely on semi-empirical or phenomenological models to account for many-body effects and thermal vibrations. Typically such models include a number of parameters which complicate fitting schemes that extract physical quantities from experimental spectra. Here we present an approach for {\it {ab initio} } calculations of these spectra starting from structure alone. A many-pole model of the dielectric function is introduced to calculate the self-energy and spectral function,\footnote{J. J. Kas et al., Phys. Rev. B {\bf76} 195116 (2007).} while a density functional theory calculation of the dynamical matrix is used to calculate effects of thermal vibrations. \footnote{Fernando D. Vila et al., Phys. Rev. B {\bf 76}, 014301 (2007).} In addition, core-hole effects are incorporated with RPA screening. \footnote{A. L. Ankudinov et al., Phys. Rev. B {\bf 71}, 165110 (2005).} This approach has been incorporated into FEFF9, a new version of the real-space multiple-scattering FEFF code for broad spectrum calculations of various optical and x-ray spectra.