The influence of experimental and model uncertainties on EXAFS results

We analyze EXAFS oscillations in k-space with the FEFF code to obtain main-shell distances Rv and mean-square displacement parameters sigma2i for all single and multiple scattering paths i in the shells v up to a maximum shell radius Rmax. To quantify the uncertainty in the determination of these model parameters we take into account experimental errors and uncertainties connected with background subtraction, with the approximate handling of the electronic many-body problem in FEFF, and with the truncation of the multiple scattering series. The impact of these uncertainties on the Rv and sigma2i is investigated in the framework of Bayesian methods. We introduce an a priori guess of these model parameters and consider two alternative strategies to control the weight of the a priori input relative to that of the experimental data. We can take a model parameter space of up to 250 dimensions. Optionally we can also fit the coordination numbers Nj (j < or = v) and the skewness of the distribution of the Rv besides the Rv and sigma2i. The method is applied to 10K Cu K-edge and 300K Au L3-edge data to obtain model parameters and their a posteriori error correlation matrices.