On Monday 03 March 2003 05:07 pm, Ahmed M Shahin wrote:
I have some question. I have mixed oxidation states and I would like to fit XANES, to determine the ratio of the mixed oxidation states I have. I looked at the documentations in the Ifeffit website but I could not find it. I have a license of feff. Would you please help me in how to fit XANES.
Ahmed, I am not sure what you mean by "fit XANES". That innocuous phrase can have a variety of meanings. My program, Athena, currently has the capability of fitting lineshapes (i.e. an arctangent and a number of Gaussians or Lorentzians) to normalized XANES data. In the not-too-distant future, Athena will be able to fit a linear combination of standards to a XANES spectrum and be able to do principle component analysis (PCA). Sam Webb's interface to Ifeffit, SixPack, already does the linear combination thing and as well as PCA. http://www-ssrl.slac.stanford.edu/~swebb/sixpack.htm Feff8 is often used to simulate XANES data. That is, one or more calculations are made and compared to the measured data. Often the Feff8 calculations are like the data in a qualitative sense more than a quantitative sense, but very often it is possible to glean information about your sample by observing hhow the calculations change as you change the conditions under which the calculations are made. That is not the same as "fitting" XANES, but it often is a useful approach. If by "fitting XANES" you mean to somehow use the local partial densities of state computed by Feff8 to compare to measured data and use that comparison to iterate the conditions of the Feff calculation until some criterion related to your data is met -- well I don't know of anyone who has written using Feff. Other researchers have done work fitting theory to XANES spectra, albeit using code bases other than Feff. Check out, for example, ** Benfatto and Della Longa, J. Synchrotron Radiat. 8 (2001) pp. 1087-1094 ** Joly, Cabaret, Renevier, and Natoli, Phys. Rev. Lett. 82:11 (1999) pp. 2398-2401 Hope that helps, B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b, X24c, U4b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/