MULTIPLE-SCATTERING CALCULATIONS OF X-RAY-ABSORPTION SPECTRA

A high-order multiple-scattering (MS) approach to the calculation of p olarized x-ray-absorption spectra, which includes both x-ray-absorptio n fine structure and x-ray-absorption near-edge structure, is presente d. Efficient calculations in arbitrary systems are carried out by usin g a curved-wave MS path formalism that ignores negligible paths, and h as an energy-dependent self-energy and MS Debye-Waller factors. Embedd ed-atom background absorption calculations on an absolute energy scale are included. The theory is illustrated for metallic Cu, Cd, and Pt. For these cases the MS expansion is found to converge to within typica l experimental accuracy, both to experiment and to full MS theories (e .g., band structure), by using only a few dozen important paths, which are primarily single-scattering, focusing, linear, and triangular.