Ab initio calculations of optical constants from ultraviolet to X-rays

We present a theory of x-ray absorption based on the real space Green's function formalism implemented in the FEFF x-ray spectroscopy code, and test it from UV to the hard x-ray limits. The one-electron theory includes self-consistent scattering potentials, core-hole and self-energy effects, and full or high order multiple scattering. From it we derive the total photo-absorption cross section summed over all edges. In contrast to standard atomic tables, the calculations include important solid-state corrections, e.g., the x-ray absorption fine structure, inelastic losses, lifetime broadening, etc. We further show that the same theory can be used to calculate the imaginary part of the complex dielectric function, from which other optical constants can be derived, e.g., the real part of the dielectric function, the complex index of refraction, and energy loss spectra. Typical results for elemental solids are presented and compared with standard theoretical tables and with experiment.