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!