Re: [Ifeffit] Cumulant expansion fittings

Hi everyone, I would like to add to Marco Vaccari's remarks that the physical quantities involved in the XAFS cumulants involve displacement-displacement correlations, e.g. and hence are sensitive to correlations in lattice directionality. Thus for example u_par and u_perp have an implicit pair of indices u_par = (vec r_i - vec r_j). hat R_ij vec u_perp = (vec r_i - vec r_j) - u_par hat R_ij and contain information about the nature of the three dimensional structure and its fluctuations in a system. As a consequence these quantities and their ensemble averages also differ from the corresponding lattice displacements in XRD. J. Rehr