TDLDA ixfc

Uses time-dependent local density approximation (TDLDA) theory to account for screening of the x-ray field and of the photoelectron–core-hole interaction. The parameter ixfc determines whether static or dynamic screening is used. ixfc=0 (static screening) accounts for screening of the x-ray field (but not the field of the core-hole), blue-shifting the spectrum. Thus TDLDA 0 works well at high energies. ixfc=1 (dynamic screening) accounts for screening of the x-ray and core-hole fields, blue-shifting the spectrum less than ixfc=0. TDLDA 1 must be used simultaniously with the NOHOLE card or else ixfc is automatically set to zero. The TDLDA card affects only module 2.

TDLDA theory takes into account polarization-type 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 L3/L2 intensity branching ratio from the 2:1 value of independent-electron theory.

See the dynamic screening paper by Ankudinov, Nesvizhskii, and Rehr (see refereces in Appendix C) for further details on the implementation of TDLDA in the FEFF calculations. See also A.I. Nesvizhskii’s thesis, Ch. 8 (pp. 82-105) for a brief description of the TDLDA theory.

* use static screening. this will only impact module 2, xsph
* use dynamic screening.
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