Density matrix calculation of optical constants from optical to x-ray frequencies

We present a theory of linear optical constants based on a single-particle density matrix and implemented in an extension of the real-space multiple scattering code FEFF. This approach avoids the need to compute wave-functions explicitly, and yields efficient calculations for frequencies ranging from the IR to hard x-rays, and applicable to arbitrary aperiodic systems. Our approach is illustrated with calculations of optical properties and applications for several materials.