Hi Andy, I have a book chapter that details how to set the k-range for a data set. It also talks about Rbkg in detail. If you want a copy just send me an email. Cheers, Shelly
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit- bounces@millenia.cars.aps.anl.gov] On Behalf Of Andy Connelly Sent: Monday, April 06, 2009 12:16 PM To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Basic questions
Some really quick basic questions. I am working with EXAFS spectra of silicate glasses at various edges (including S and Fe K edges) and I am having a really difficult time pinning down the structures. Clearly with glasses I can't always be sure of the oxygen co-ordination and so I have to refine this value which is one among many problems. Just to check I have things right:
1. Are there any problems if I set the R-range min to the same value as Rbkg?
2. If I want to refine the degeneracy of a path can I write the expression "amp*N_1" in the SO2 box? (where the N box is set to 1) and then refine "amp" and/or "N_1"? where N_1 equivalent to the degeneracy and amp is effectively SO2. Clearly they will be highly correlated, but does a formula like this cause IFEFFIT any problems?
3. If, for initial fits, I am only interested in the first shell should I set R-range max to a lower value to isolate that shell and then increase it as I look at shells at longer distances?
4. If I have a calculated Fe3+-O path from a 4 and 6 co-ordinate reference are these equivalent? Obviously, they will give a different bond length and the MS paths will change but if I am only fitting a first shell is there anything different. I think the answer involves the muffin tin potentials but I'm a little out of my depth there.
Any advice about solving glass structures more than welcome. Whatever I try I can't get realistic results out.
Thank you for your time,
Andy Connelly _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit