TDLDA theory takes into account polarizationtype many body effects (i.e., polarization of the electronic charge) which screen the local x-ray field. These effects are most important for xrays with energies less than 1 keV, hence TDLDA 0 works well at high energies. The screened interaction is calculated partially based on the Bethe-Salpeter equation, in the basis of local atomic states. This approximation yields efficient calculations of the spectra in terms of screened transition matrix elements. Note that TDLDA does not account for core-hole relaxation effects.
L-shell x-ray absorption in 3d transition metals is sensitive to dynamic screening effects. For rare-gas solids, dynamic screening accounts for deviations of the / intensity branching ratio from the 2:1 value of independent-electron theory.
See the paper on dynamic screening by Ankudinov, Nesvizhskii, and Rehr for further details on the implementation of TDLDA in the FEFF calculations. See also A.I. Nesvizhskii's thesis, Ch. 8 (pp. 82-105, available on the FEFF webpage, see http://feff.phys.washington.edu/) for a brief description of the TDLDA theory.
* use static screening. this will only impact module 2, XSPH TDLDA 0