You are both mistaken, but do not check what FEFF is on Urban Dictionary, as it is inappropriate. Anatoly ________________________________ From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Ravel, Bruce Sent: Tue 5/10/2011 3:16 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] What does FEFF stand for? On Tuesday, May 10, 2011 03:03:23 pm Scott Calvin wrote:
My understanding, although I could be wrong is that the "effective" part came from an improvement of the theory to account for curved-wave effects. In other words, early theories approximated the photoelectron as a plane wave, but of course it spreads out radially from the absorbing atom. That change necessitated tweaking the definitions of the factors, so it became the "effective" f.
I think you are mistaken. My memory of the etymology has to do with the formalism dating back to Feff5 for computing MS paths. For a purely single scattering theory, you have an F and a phi (without the subscript eff). That is, you can simply compute the scatting function for the one scatterer and be done with it. Feff's path expansion introduced two clever things to the EXAFS business. One is that it provided a formalism for computing a single function that takes into account the angle-dependent scattering functions of all atoms in an arbitrary-geometry multiple scattering path. This allows one to treat a MS path with the familiar SS EXAFS equation only by replacing F and phi with F_eff and phi_eff. That innovation is central to how Ifeffit works. The second clever thing is that it's really fast. That's not such a big deal today, but back in the mid-90s, when a Feff run could take several minutes, a faster algorithm was very welcome indeed. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit