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

Abstract

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 photoabsorption cross section is calculated using the full multiplescattering 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.

Solvation Sphere of I- and Br- in Water

“…Experimental XAS spectra were theoretically modeled using MXAN, which performs full multiple scattering analysis to obtain structural information [8], [9]. Starting structures were taken from the best three-dimesional models that included the coordination numbers 4, 6, 8, and 10 with radial metrics obtained from EXAFS analysis.…”

“…EXAFS fits were used to test structural models (4,6,8, and 10 coordinate geometries), which were subsequently used to fit the near-edge data. MXAN has the advantage that it mostly independent of thermal noise/Debye-Waller factors, which lead to EXAFS signal dampening and broadening.…”

“…MXAN has the advantage that it mostly independent of thermal noise/Debye-Waller factors, which lead to EXAFS signal dampening and broadening. Near-edge analysis was performed using MXAN, a data analysis software that employs full multiple scattering theory, to reproduce the x-ray absorption near edge spectrum (XANES) and the EXAFS region out to 150 eV, using input structural and nonstructural parameters [8], [9]. The near-edge analysis used by MXAN is very sensitive to local geometries and can furnish accurate three-dimensional structural information [8], [9], [6].…”

Unusual proximal heme pocket geometry in the deoxygenated Thermobifida fusca: A combined spectroscopic investigation

“…Recent theoretical advances have made the extended X-ray absorption fine structure (EXAFS) analysis a primary, well established structural tool to investigate bond lengths at a precision of about 0.02 Å [9]. Moreover, a quantitative X-ray absorption near edge structure (XANES) analysis has been developed [10,11] and applied in combination with EXAFS to different system to extract information on bond distances and angular…”

“…The XANES calculations have been performed using the MXAN software procedure [8,10]. The analysis of the XANES spectra has been carried out using a cluster of thirty-one atoms, i.e., the porphyrin macrocycle, the histidine imidazole, and the oxygen of an unbound water molecule.…”