[Ifeffit] Rutile Rbkq remove question.

Carlo Segre segre at iit.edu
Sat Mar 15 14:05:26 CDT 2008

Hello Pei:

On Sat, 15 Mar 2008, Richard Mayes wrote:

> As for why the feature (low-R junk) increases as Rbkg is adjusted from 1.0
> to 1.21 but disappears at 1.22, I'm not sure but my guess is that this is
> an artifact of removing some of the data that contributes to the feature,
> and by 1.22 you have removed enough that the feature disappears (hopefully
> someone will correct me if I'm wrong).  I would be weary of using an Rbkg
> of 1.22 though (as I think you see why in the plots - Question 3).

I think that Rbkg=1.22 is generally a bit too high for comfort is your 
first shell distances are fairly short.  In my opinion, you should set 
Rbkg below 1.0, in the regions where the low-R peak first disappears.  Try 
changing Rbkg by 0.02 at a time while looking at the k^3 weighting.  There 
is usally a point at which you see a significant reduction in the 
background peak and then not much more change for a while.

The other thing you can do is to model the data with Rbkg=0.9 and 1.22 to 
see how the fit results compare.  This might help you figure out the 
best way to handle these data.



Carlo U. Segre -- Professor of Physics
Associate Dean for Special Projects, Graduate College
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://www.iit.edu/~segre   segre at debian.org

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