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Feffit Home Page

FEFFIT is a computer program for the analysis of XAFS data. It is designed to fit experimental XAFS spectra to theoretical calculations from FEFF.
FEFFIT is fairly easy to use. Fitting can be done in k or R space, and error analysis is automatically done, and a wide-range of options are given for modelling XAFS data.

The current FEFFIT version is 2.98
The code was last updated on Sep 18, 2002

The latest version of the source code and Windows Executable are available for download here .

The Program Documentation is available in postscript.

The best reference for FEFFIT is

Analysis of multiple-scattering XAFS data using theoretical standards ,
M. Newville, B. Ravel, D. Haskel, J. J. Rehr, E. A. Stern, and Y. Yacoby,
Physica B208&209, p154-155 (1995)

Recent Changes to FEFFIT

R-factor calculation improved

fitting in back-transformed k-space now works reliably.

relaxed rules for ascii data files.

fixed a sign error in interaction of mean-free-path with disorder terms.

Fourier Transforms sped up by storing window function between calls.

Support of simultaneous fitting of more than one data set. see "extra" (postscript) documentation.

Output file feffit.prm contains additional formatted output of the path parameters *and their uncertainties*.

The number of independent points is now a floating-point number.

background-removal correction (ala autobk) added. "bkg=true" now uses information below Rmin to "improve" background removal. Output files "*k.bkg" give the background function used. Using "bkgfile = file_name" will use that file (eg, from a previous "bkg=true" run) to clean up data at low-R. Mostly cosmetic, this works marginally well.

played with several different variations of "tranquada correction", deciding that it was best to do as originally described: deltar -> deltar - 2 sigma2/ reff

logical flag "kfull" will cause the writing of complex chi(k). the default is to write the real part only.

the comment character for ascii data files can be set using keyword "comment = #" etc. "#" is the default.

the total number of comment lines can be set with keyword "mdocxx". All files will have this many title lines, even if empty lines are needed.

added option for phase-corrected Fourier Transforms. The phase dependence of the first feffn.dat file listed is used to alter chi(k) to be chi(k)_pc = chi(k) * exp(-i * phase(k)) where phase(k) is the sum of columns 2 and 4 from feffnnnn.dat. Keyword "pcout" causes these PC-FT's to be done on output.

added support of the ascii feff.bin from feff702m / feff7023 (Matt's own version of feff -- never officially released).

added support for "include" files -- files which contain additional feffit.inp commands. syntax is "include file" on its own line in feffit.inp. Can be used nested, but not used recursively.

Feedback and questions concerning this web site should be sent to newville@cars.uchicago.edu
Last modified: May 21, 2007