Everyone is at least partially right. In our PR B34,4350(86) paper (which was rejected by PRL) we noted that the exact single scattering XAFS eq. could be recast in the same form as that of Sayers Stern & Lytle (PRL 27,1204(71) by replacing the backscattering amplitude f(pi) with the exact curved wave expression given by ~f (see our Eq. 9). For single scattering this ~f is equivalent to the Z factor in Lee and Pendry and a similar quantity in Schaich. We replaced ~f with f_eff (i.e., the effective scattering amplitude)in our PRB 44, 4146 (91), which also describes the single-scattering FEFF code. This code started in pieces at Los Alamos in 1984, but the integrated version with a reliable overlapped atom potential became FEFF3 some years later. The name FEFF originated during a meeting with Jose Mustre de Leon, Steve Zabinsky and others (?) when we were looking for a catchy name for the code. Although it was not an acronym, I thought FEFF seemed quite appropriate. Interestingly, we found that one can also define an exact effective scattering amplitude for multiple-scattering paths, e.g. as in PRL 69, 3397 (92). The beauty of this representation is that permits an interpretation of both single- and multiple-scattering contributions using the standard EXAFS equation. Thus in subsequent papers and code developments we simply used f_eff to describe all SS and MS paths. Thus the name FEFF was also retained for subsequent versions of the code. J. Rehr On Tue, 10 May 2011, Francisco Garcia wrote:

Dear all,

I wish to ask a somewhat novice question: What does the acronym FEFF stand for?

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