Ahmed, I trust you do not mind that I answer your question on the ifeffit mailing list. It seems of sufficiently broad interest that an answer in that forum is appropriate. You asked: AS> I received a note with the latest version of your software. In my AS> understanding that the latest version includes the Feff6L without AS> a license fee. Does this mean that by downloading the latest AS> version of ifeffit, so that I do not need to buy a license of AS> feff? Well, my answer is ether a qualified yes or a qualified no, depending on what your interests are ;-) *IF* you are interested only in the extended EXAFS features of Feff and *IF* you do not think that you need any of the more recent developments of Feff (most notably, self consistent potentials), then you probably do not need a license for Feff. Feff6L is free in both senses of the word -- it doesn't cost you any money and you may freely use, modify, and redistribute the code under the terms of its license. See this post from John Rehr to the mailing list about the Feff6L license: http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2002-November/000169.html However, if you are interested in computing XANES, partial electronic densities of state, charge transfer or ab initio Fermi energies, you will need to license a copy of the latest version of Feff. If you are interested in the latest developments of such theoretical topics as self-consistent potentials, improved self-energies, S02 calculations, resonant scattering corrections, or a whole host of other features available in the latest Feff and not available in Feff6L, you will need to license a copy of the latest version of Feff. Feff6L is useful code for the extended exafs practitioner. If that were not true than Matt would not have been so effusive in his post yesterday announcing Ifeffit 1.0075. While Feff6L is useful and usable for exafs analysis, you must be aware that it is largely limitted to exafs analysis. If you need XANES calculations, you need a Feff8 license. All clear? 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/