[Ifeffit] Negative ss problem

Chris Patridge cpatridge8407 at gmail.com
Wed Jul 14 06:45:57 CDT 2010


It seems to me that you have some more problems than just ss values.   
The data collection range seems a little short just ~300 eV past the  
edge. Amp is quite high and delr is very large. I am an expert by no  
means but I might suggest that you have the wrong model. The model is  
trying to compensate for high R space magnitude by making amp above 1  
and ss negative.  Have you considered your data processing in Athena?   
Did you use the default settings?  I would guess Cu-O bonds might be  
too short for the presets in Athena. How did you check your model?

Buena salud,

Chris Patridge

On Jul 14, 2010, at 2:59 AM, Abhijeet Gaur <abhijeetgaur9 at gmail.com>  

> Hi all,
>          I read the discussion on negative Debye waller factor. As  
> per the discussion the negative value of this factor shows that the  
> model has shortcomings, so it should be corrected.
>         I am also getting the same problem while fitting one of my  
> samples. It is a Cu complex whose EXAFS data is taken at Dispersive  
> EXAFS beamline at RRCAT, Indore, India.
>        In the complex the nearest neighbours of Copper atom are  
> Nitrogen and Oxygen.
>        I am getting a very good fit upto 3rd shell but the problem  
> is that all ss parameters are coming negative. I checked the model  
> it seem correct.
>        Also I am getting a peak below 1 Angs which is also getting  
> fitted but I am not able to get that whether it is a real or due to  
> some noise.
>        I am attaching herewith the results of data analysis and  
> fitting.
>        Thanks in advance
>        With regards
>     Abhijeet Gaur
> Vikram University
> Ujjain, INDIA
> <Cu complex fitting results.doc>
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