[Ifeffit] Rbkg value

Scott Calvin SCalvin at slc.edu
Fri Oct 23 15:24:39 CDT 2009

Hi Chris,

One thing to keep in mind is that it is not wrong to eliminate part of  
your signal; it just means you're losing a little bit of data. This is  
similar to a common filtering mistake that beginners make when trying  
to choose the maximum end of their fitting range: they look at the  
paths they are including, and try to set Rmax high enough to include  
most of the contribution from the paths they are including. What they  
should be doing, however, is to look at the paths they are not  
including, and set Rmax low enough so that the contributions from  
those paths are tolerably small.

Looking at correlations between background parameters and fitted  
parameters when the "fit background" option is selected also helps  
provide you with information. I'll admit that the "fit background"  
button confuses me a bit, though (I always have to spend ten minutes  
convincing myself again as to what exactly it is doing), so someone  
else should explain how that can be used to help address your question.

--Scott Calvin
Sarah Lawrence College

On Oct 23, 2009, at 3:51 PM, Chris Patridge wrote:

> Hello everyone,
> In removing background, most literature suggests Rbkg value of 1.0  
> because below this represents mostly noise and low freq components  
> not part of the scattering effect.  In using Feff and viewing the  
> individual paths calculated a number of them have paths near 1.5 A,  
> therefore meaning that they have some contributions very close to  
> 1.0 A and below in R space due to phase shift.  Has anyone modeled  
> materials which contain these rather short Reff and how did you  
> decide what was scattering and noise?
> Thank you all,
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