# Main Page

## FEFF

FEFF is an automated program for ab initio multiple scattering calculations of X-ray Absorption Fine Structure (XAFS), X-ray Absorption Near-Edge Structure (XANES) and various other spectra for clusters of atoms. The code yields scattering amplitudes and phases used in many modern XAFS analysis codes, as well as various other properties.

•FEFF 9: The newest version is FEFF9 (Version 9.03 beta) FEFF 9 has a variety of new features and options. First there are several new spectroscopies which can be calculated with FEFF 9, including electron energy loss spectra (EELS) and non-resonant inelastic x-ray scattering (NRIXS). In addition, there are a variety of improvements. These include; (1) ab initio Debye-Waller factors; (2) improved treatment of inelastic losses; (3) an improved treatment of the core-hole interaction; and (4) more accurate treatment of crystalline systems with k-space calculation of the Green's function. FEFF9 comes with the JFEFF GUI.

•FEFF 8: FEFF 8 improves over previous versions of FEFF by including self consistent calculation of potentials to provide charge transfer and a more accurate estimate of the Fermi level. It also includes full multiple scattering calculations to improve XANES calculations, where multiple scattering expansions can fail to converge. FEFF 8 can output the angular momentum projected density of states, x-ray emission spectra and x-ray scattering amplitudes. The improvements in FEFF 8.40 simplify spin-dependent calculations and can include improved treatment of core-hole and local field effects. FEFF8 now includes JFEFF, a graphical front-end for FEFF 8.4.

•ATOMS: Generates input files, feff.inp, for crystalline materials which are suitable for FEFF5 and higher (included with FEFF).

$\chi(k) = S^2_0 \mathcal{R}\sum_{shells}\frac{N F_{eff}}{k R^2}\exp(-2r/\lambda)\sin(2kR+\phi_{eff}+\phi_c)\exp(-2k^2\sigma^2)$