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 R_ν and mean-square displacement parameters σ_i² for all single and multiple scattering paths i in the shells ν up to a maximum shell radius R_max. 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 R_ν and σ_i² 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 N_j (j≤ν) and the skewness of the distribution of the R_ν besides the R_ν and σ_i². 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.