Thank you Dominik, I have had a play around with the data and this model is definitely the better model. Just a sidenote, is the general workflow for fitting XAFS data the following: Fit first shell and get reasonable Enot and Amp and then make set them, then incrementally add more of the scatter paths and adjust the delR for each path correspondingly. Adjusting degeneracy for atom assuming there are slight differences in the atoms spacing. I know the question is very trivial but I don't seem to be able to find a general guideline for knowing when the fitting process is over in these type of analysis. Many thanks, Nic -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Dominik Samuelis Sent: Tuesday, 2 August 2011 7:15 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Question on GDS values: amp Dear Nic, I've had a short look into your Artemis file. First of all, it seems that something's wrong with the Gd2O3 structure data in your feff.inp. Running feff on your feff.inp gives this error: Feff 8.40 ... WARNING: TWO ATOMS VERY CLOSE TOGETHER. CHECK INPUT. atoms 8 14 8 2.24848E+00 2.70250E+00 0.00000E+00 14 2.47549E+00 2.70250E+00 0.00000E+00 Run continues in case you really meant it. WARNING: TWO ATOMS VERY CLOSE TOGETHER. CHECK INPUT. atoms 9 15 9 -2.24848E+00 -2.70250E+00 0.00000E+00 15 -2.47549E+00 -2.70250E+00 0.00000E+00 Run continues in case you really meant it. [...] It seems that all your "Gd2" atoms have a duplicate in your "Gd3" atoms, shifted only by ~0.2 angstroms in either x,y, or z direction. Looking further at your feff.inp, already your ATOMS input somehow looks broken: (your ATOMS list) * Gd 0.25000 0.25000 0.25000 Gd1 1.00000 * Gd 0.02100 0.00000 0.25000 Gd2 1.00000 * Gd 0.54200 0.00000 0.25000 Gd3 1.00000 * O 0.12500 0.12500 0.37500 O1 1.00000 * O 0.12500 0.37500 0.37500 O2 (my list, cif file from ICSD, Shuenn et al., J. Chin. Chem. Soc. 57 (2010), 938) Gd 0.25 0.25 0.25 Gd1 1.000 * (8b position) O 0.3904 0.1513 0.379 O1 1.000 * (48e position) Gd 0.9710 0 0.25 Gd2 1.000 * (24d position) Using this crystal data, I was able to fit your data reasonably well (didn't tweak to make the fit perfect though...) - see attached file! I've also attached the .cif file that I've used, in case you want to compare with yours. BTW, enot values of >20 eV shouldn't really happen in any fit. Best regards, Dominik On 02.08.2011 04:42, Nicholas.Tse@csiro.au wrote:
Thank you all the suggestions.
I believe the ATOM model used is representative of what it should be. I generated the FEFF file from the CIF file from the American Mineralogist X'stal DB. The generated FEFF has the edge L3 that should be fine. A simple summation of the scatter paths does roughly produce the pattern for the sample, except for the amplitudes.
The enot was found to be 53.8995 +/- 2.7632.
I have also included the .prj and .apj files for your inspection.
Regards,
Nic
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- Dr. Dominik Samuelis d.samuelis@fkf.mpg.de Max-Planck-Institut für Festkörperforschung Max Planck Institute for Solid State Research Heisenbergstr. 1 70569 Stuttgart Germany Phone +49-711-689-1769 Fax +49-711-689-1722 Web http://www.fkf.mpg.de/maier/