# 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 9.7.1 -- however this wiki site was last updated for a slightly older version of FEFF9). 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 includes JFEFF, a graphical front-end for FEFF 8.4.

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

## About the FEFF wiki

The FEFF wiki is intended for current users and developers of the FEFF code. It contains documentation and information on running the FEFF code. All other information - such as how to order the code, where to download it, a list of publications, and so on - can be obtained at the FEFF project homepage. These pages are accessible through the "feff project" menu in the sidebar of this wiki. The PDF documentation on the FEFF project homepage is slightly more up-to-date than this wiki site.

To avoid spam, we ask that you register before posting content on the FEFF wiki. Please find instructions for registration via the "becoming a FEFF wiki author" link in the sidebar.

## FEFF Documentation

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