Thanks for the message. I guess what I wanted to say was that from what I understand due to lifetime effects the "effective" radius about the absorbing site for which the outgoing scattered wave "exists" is on the order of 2 nn (I have big lattice constant material). It would seem to me then that the inequivalent sites being physically separated by more than this distance (we are talking about crude approximations here) would not interfere. In reality, with bond lengths on the order of 3 Angstroms and 2nn along the lines of 4.5 Angstroms, my case is somewhere in between the coherent interaction and the dilute dopant -- e.g. every site is by itself -- extreme. Certainly, in the latter case it would be wrong to add the signals together coherently! What is the consensus for this sort of thing? The different E0's is a good point too. Paul On 2005/01/14, at 16:16, Scott Calvin wrote:
Hi Paul,
Actually, the inequivalent sites do interfere coherently. EXAFS chi's aren't like quantum mechanical wave functions, for which only relative phase matters. The phase gives information about E0, and that's a physically meaningful quantity. In other words, if one of the sites is producing a peak at 7200 eV and another is producing a trough, they will tend to cancel.
So yes, Artemis and Ifeffit do the right thing, but the right thing is to add everything up coherently regardless of which feff calculation it comes from.
A few other notes on this kind of fit: you must, of course, weight the amplitudes of each feff calculation by the relative number of sites of that type. Also, it is quite possible that you'll need different e0's for the different sites.
--Scott Calvin Sarah Lawrence College
A simple question. I am have been doing multiple edge fits of different materials for a while in artemis (diana). Now, I would like to analyze a material with inequivalent sites for one of the edges. I understand how to read in the data and have read in the different feff calculations (for each inequivalent site), but what I just want to confirm that artemis/diana/ifeffit will do the "right" thing, namely coherently add the contributions *within* each feff calculation and add the intensities of each feff calculation -- e.g. I don't think there is any interference between the XAFS signal on different crystallographic sites -- or even if there is it is ignorable at least for first neighbor interactions. If there is anyone out there with experience in doing this (or is the right thing done automatically?), drop me (or the list) a line. Thanks a lot!
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Dr. Paul Fons Senior Researcher National Institute for Advanced Industrial Science & Technology METI Center for Applied Near-Field Optics Research (CANFOR) AIST Central 4, Higashi 1-1-1 Tsukuba, Ibaraki JAPAN 305-8568 tel. +81-298-61-5636 fax. +81-298-61-2939 email: paul-fons@aist.go.jp The lines below are in a Japanese font 〒３０５−８５６８ 茨城県つくば市東１−１−1 つくば中央第４ 近接場光応用工学センター ポール・フォンス主任研究官