DIFFKK is a program to convert XAFS (or XANES) mu(E) to the anomalous scattering factors, f1(E) and f2(E).
This can be useful for DAFS work or for anomalous x-ray scattering work in which the "solid-state" (aka XAFS-like) components are important.
The Fortran source code, documentation, and a worked example for DIFFKK can be found at http://cars9.uchicago.edu/dafs/diffkk/
The Python source code, which uses IFEFFIT, is meant to be a complete replication of the Fortran source code. The translation by Adam Webb is
Older documentation is here
The work is described in the paper
J. O. Cross, M. Newville, J. J. Rehr, L. B. Sorensen, C. E. Bouldin, G. Watson, T. Gouder, G. H. Lander, and M. I. Bell. Inclusion of local structure effects in theoretical x-ray scattering amplitudes using ab-initio x-ray-absorption spectra simulation. Physical Review B, 58 pp. 11215, 1998.