Re: [Ifeffit] Linear Combination Fitting using ATHENA
Hello, maybe that fingerprinting technique would be Mossbauer spectroscopy. The Fe(II)/Fe(III) ratio comes easily and also there are lots of papers about Mg-ferrite, an example: 10.1109/TMAG.2009.2018880 http://dx.doi.org/10.1109/TMAG.2009.2018880 Alexandre. ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Re: [Ifeffit] Linear Combination Fitting using ATHENA
I would say that the Mossbauer isn't always quite straight forward, especially if the OP is working with nanoparticles. You have to find the right temperature where superparamagnetism is gone but the Verwey transition hasn't occurred to reliably fit the resulting Mossbauer spectra. (I'll assume from ignorance that that Mg-ferrites have Verwey transitions.) I would think the two best end-members for the XAS LC fits are possibly magnetite (fully stoichiometric: Fe2+/Fe3+ = 0.5) and either maghemite (gamma-Fe2O3) or the fully oxidized Mg-ferrite. Which Fe2O3 are you using Teck Kwang Choo? If you are using the alpha-form (hematite) then I would suspect you might not get very good fits as the structural difference between maghemite and hematite significantly influence their XANES spectra. I've had good success finding Fe2+/Fe3+ ratios in partially oxidized magnetites by using magnetite and maghemite as end-members in LC fits. So I think you should have reasonable success for the Mg-ferrites using the right end-members. Contact me in person below, if you are interested in magnetite/maghemite standard spectra. Best, Drew Latta --- Drew E. Latta, Ph.D. Postdoctoral Associate Molecular Environmental Science Group Biosciences Division Argonne National Laboratory Building 203, Room E-105 9700 South Cass Avenue Argonne, IL 60439 Phone: 1-630-252-3985 dla...@anl.govmailto:dla...@anl.gov http://www.mesg.anl.gov --- From: ifeffit-boun...@millenia.cars.aps.anl.gov [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] On Behalf Of Alexandre dos Santos Anastacio Sent: Monday, August 12, 2013 9:01 AM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Linear Combination Fitting using ATHENA Hello, maybe that fingerprinting technique would be Mossbauer spectroscopy. The Fe(II)/Fe(III) ratio comes easily and also there are lots of papers about Mg-ferrite, an example: 10.1109/TMAG.2009.2018880http://dx.doi.org/10.1109/TMAG.2009.2018880 Alexandre. ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
[Ifeffit] issues with Athena (new Demeter package)
Hi All, I experience two issues with Athena of the updated new Demeter package, which it would be easier to describe: 1) when I open successively two .prj files that contain each a fitted spectrum, Athena seems to remember only the positions, widths and amplitudes of arctan and gaussian curves of the spectrum I open first; this translates to the fact that for the other fitted spectra that I open afterwards, it remembers the peak positions, widths and amplitudes of the curves belonging to the initially opened spectrum. The result of this issue is that I need to enter manually each time these values in order to get the fits back again - do you have any suggestions how this can be fixed?; 2) another issue is that after spectra calibrations, the spectrum does not appear to be calibrated. More specifically, when one checks the centroid positions of arctan or gaussian curves directly on the spectrum, the values don't correspond with the ones in the boxes, which I believe that means the calibration did not happen after all. Thank you very much in advance for any suggestions or ideas! Best wishes, Adrian *** Adrian Gainar PhD student Office: D37 School of Chemical Engineering and Analytical Science Jackson's Mill University of Manchester Manchester M13 9PL UK e-mail address contact: adrian.gai...@postgrad.manchester.ac.ukmailto:adrian.gai...@postgrad.manchester.ac.uk office telephone no.: +44(0)161 306 4362 ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Re: [Ifeffit] Recommendations for DFT/computational chemistry software?
Hi Scott, Gaussian is a pretty solid program. The input files are easy to write, and it's popularity make it easy to find support. It is a commercial product, though, which can be a problem if your on a tight budget. Several years back, I tried Gamess, which worked fine. Its biggest drawback for me was writing input files. It was cumbersome to use mixed/custom basis sets, which is probably key for anything you'll be doing for EXAFS. I haven't tried Gamess recently, so the situation may have changed. I hear good things about Orca as well. I think this package does a lot of interesting stuff related to XAS, but I haven't spent much time with it. A couple years back, Orca couldn't do analytical frequency calculations, which, in my experience, led to very slow frequency calculations. However, according to the website, it seems like that feature will be coming soon, so I would like to find some time to really play around with this program again. My colleague uses WebMO, which is a web-based frontend to many electronic structure packages. I haven't used it myself, but it may make for a more unified experience for many of these packages. Just my two cents... Good luck. Ryan Hi all, I know many of you use DFT calculations to help model EXAFS data for molecular compounds. Do you have recommendations for good computational chemistry packages, commercial or otherwise, to use for that purpose? --Scott Calvin Sarah Lawrence College ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
