June 2015 - Ifeffit - millenia.cars.aps.anl.gov

low and negative ss2 and bug in the log file of fit history
by Raj kumar 01 Jun '15

01 Jun '15

Dear All, I am trying to fit the first shell FT of bulk YbVO4 (measured in dispersive EXAFS) with the reference YbVO4. The resultant SS2 value for the first shell is found to be low for wide k-range selection, whereas approaching negative for the relatively short k-range window. While approaching negative value (of ss2), i have tried to constraint the ss2 value using expression abs(ss). In that case, ss2 value is found to take value 0. Please help me to figure out the problem. Further i have found a small bug in the fit history window. After each fit, earlier data set in the log file of fit history is found to overwritten with the latest fitting parameters (like k range, dk, etc..). Here in my log file window, all fit data set contain the same data set value as like the last fit (fit9). Regards, Raj

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Re: [Ifeffit] Mn3O4 EXAFS fitting
by 이국승 01 Jun '15

01 Jun '15

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Re: [Ifeffit] Mn3O4 EXAFS fitting
by fred.mosselmans＠diamond.ac.uk 01 Jun '15

01 Jun '15

Dear Kug-Seung Your main initial problem is you didn't understand the structure of Mn3O4. It is a spinel with two Mn sites one octahedral and one tetrahedral. You need to consider both sites to have a chance of fitting, and set multiplication factors on the relative amps in the ratio. It has 1/3 tetrahedral sites and 2/3 octahedral. You need to do the feff calculation twice with each site as the core atom. In the attached project I have done this. You then end up with a lot of paths so to try to restrict the no of variables I have made several of sigma squared to be the same. I am sure this model could be improved upon but I wanted to show you how to get going in fitting the structure. In theory as the Mn tetrahedral site and octahedral sites are different oxidations states they might (should) have different E0s as well but with a limited data range this gets hard to test properly. Best wishes Fred Mosselmans Message: 1 Date: Mon, 01 Jun 2015 15:59:40 +0900 From: ??? <lks3006(a)postech.ac.kr> To: ifeffit(a)millenia.cars.aps.anl.gov Subject: [Ifeffit] Mn3O4 EXAFS fitting Message-ID: <1433141980110.23146.postech(a)postech.ac.kr> Content-Type: text/plain; charset="us-ascii" An HTML attachment was scrubbed... URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20150601/4ec…>

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Re: [Ifeffit] _Mn3O4 EXAFS fitting
by 이국승 01 Jun '15

01 Jun '15

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Mn3O4 EXAFS fitting
by 이국승 01 Jun '15

01 Jun '15

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