Geometrical fitting of experimental XANES spectra by a full multiple-scattering procedure

In this paper a new software procedure is presented, named MXAN, able to fit the XANES part (from the edge to about 200 eV) of experimental X-ray absorption data. The method is based on the fitting between the experimental spectrum and several theoretical calculations generated by changing the relevant geometrical parameters of the site around the absorbing atom. The X-ray photo-absorption cross section is calculated using the full multiple-scattering scheme; different choices of the exchange correlation part of the potential can be utilised. To show the potentialities of the method the analysis of the nickel K-edge of the nickel ion in aqueous solution is presented. The procedure is able to recover the correct information on the symmetry and atomic distances from the experimental Ni K-edge XANES spectrum. The recovered structure is found to be independent of the starting conditions, showing the theoretical uniqueness of the structural solution.