THEORETICAL X-RAY ABSORPTION FINE-STRUCTURE STANDARDS

Theoretical X-ray absorption fine structure (XAFS) standards are developed for arbitrary pairs of atoms throughout the periodic table (Z less-than-or-equal-to 94). These standard XAFS spectra are obtained from ab initio single-scattering XAFS calculations, using an automated code, FEFF, which takes into account the most important features in current theories: (i) an exact treatment of curved-wave effects; (ii) approximate molecular potentials derived from relativistic atoms, (iii) a complex, energy-dependent self-energy; (iv) a well defined energy reference. FEFF also yields tables of XAFS phases and amplitudes as well as mean-free paths. Sample results are presented and compared with experimental results and with earlier work. We find that these theoretical standards are competitive with experimental standards, permitting XAFS analysis at lower wavenumbers and yielding distance determinations typically better than 0.02 angstrom and coordination numbers typically better than 20%. These standards also provide theoretical tests of chemical transferability in XAFS.