[Ifeffit] EXAFS Fitting with 2 CIF files

[Matthew Marcus]

Extending what Scott said, I find it useful to make the coefficients 
abs(fracoxide) and abs(1-abs(fracoxide)) to avoid false minima with 
negative S0^2.
	mam

On 9/4/2021 1:21 PM, Scott Calvin wrote:
> Hi Zihao,
> 
> Do it by folding the molar ratio in to the amp parameter for each CIF. Of course S02 is part of that parameter, too.
> 
> So the amp for PtO2 might be parameterized as S02 * fracoxide and the amp for Pt3Fe as S02 * (1-fracoxide)
> 
> You could either assume the S02 is the same for the two phases (as I implicitly did by writing it with only one S02 variable), or you could use a standard for each (from a sample prepared and measured in a similar way) to fix the S02 for each phase.
> 
> Best,
> Scott Calvin
> Lehman College of the City University of New York
> 
>> On Sep 4, 2021, at 4:02 PM, Zihao Yan <zihao.yan.sci at gmail.com> wrote:
>>
>> Dear Ifeffit members:
>>
>> I have a sample which is a mixture of PtFe and PtO2. In order to do the EXAFS fitting, I imported 2 CIF files on Artemis and generated the following 3 paths:
>>  From PtO2: Pt-O @ 2.07 nm
>>  From Pt3Fe: Pt-Pt @ 2.736 nm, Pt-Fe @ 2.736 nm
>> Then, I used these 3 bonds to do the fitting as in the online tutorial (which used 1 CIF file). The fitting result is good in terms of R^2 but it is not scientifically correct.
>>
>> I think I didn't set up a parameter which determines the ratio between CIF(PtO2) and CIF(Pt3Fe). I mean there should be a parameter that regulates how much each CIF contributes to the fitting or the molar ratio between PtO2 and Pt3Fe in my system.
>>
>> Could someone please give me some suggestions on how to do EXAFS fitting with 2 CIF files? Is there anywhere I can set up the molar ratio between PtO2 and Pt3Fe?
>>
>> Yours sincerely,
>> Zihao Yan
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