Modeling of XANES-spectra with the FEFF-program

Abstract

The aim of this project is the calculation of the absorption coefficient μ of X-ray absorption spectra as a function of energy and a comparison with experimental data. A characteristic fine structure can be found in X-ray absorption spectra (XAS) consisting of the XANES (X-Ray Absorption Near Edge Structure) and the EXAFS (Extended X-Ray Absorption Fine Structure) region. XANES is characterized by multiple scattering and provides information about coordination chemistry and bonding angles of the irradiated sample. The program FEFF 8.4 was used for the calculations of the absorption K-edge spectra. FEFF was generated for ab initio multiple scattering calculations of X-ray Absorption Fine Structure (XAFS) of atom-clusters. The code yields scattering amplitudes, phases and other quantities. We computed μ at the K-edge of several elements like Ti, S and Fe. For this purpose, clusters of Na2SO4, Ba2TiO4, FeS2, CaSO2 2(H 2O) were used, working with several space groups. Some of the calculations are consistent with the results of the experiments, but others show energy shifts in the range of some eV. In summary, the FEFF calculations and the experimental data exhibit similarities as well as deviations. By using trimming parameters, deviations could be eliminated to a certain extent, which will be presented. © 2009 IOP Publishing Ltd.