[Ifeffit] Normalization in Athena

[Gudrun Lisa Bovenkamp]

Hi everybody,

I am sure that Athena was tested a lot, but as Jeremy pointed out, 
which I think now is the answer: If the background is substracted 
before the fitting of the post edge. That is actually how we are 
normalizing XANES data in our group and that is what I tried in 
Athena.
It is actually working much better with 2. order norm and flattening.
Since I do not want to do it by hand for all spectra and import them 
back into Athena for LCF.
This time I attached a the example Athena project file.
But with this approach I rarely get the spectrum oscillating around 
one.
I will think about it.

Thanks for the hint, Matt, about "no points" in the range. But Athena 
is acutally complaining, if there are no points to fit the line.


Of course, I read the chapter on Normalization in Athena. And what is 
giving me trouble, why I try the "1-point" approach, is that the small 
differences in the first post-edge normalization point make a great 
deal of difference in the normalization of the spectra respective to 
each other and thus LCF.


Finally, I believe it is a very interesting question of taste how to 
determine the edge step for XANES data or when to substract the 
background. Or is there any specific reason for a special approach?


Thank you all for your help!!
Greetings,
Lisa

  
> Hi Lisa,
> 
> Be sure that Athena has been rigorously tested and she does know how 
>to
> normalize data. It is much more likely that the default values are 
>not
> the "best" ones for your data.
> 
> My book chapter goes over how Athena normalizes data in detail.  If 
>you
> send me your email address I'll send you a copy. In particular see
> figure 14-16.
> 
> Cheers,
> Shelly


> 
> Shelly,
> 
> I agree that Athena applies its (her) algorithm correctly.  Whether 
>that
> algorithm is correct may be a matter of opinion.  The apparent
> discrepency Lisa sees is due to Athena's algorithm:
> 
> i.e., fit preedge line, fit postedge function to normalization 
>range,
> extrapolate both functions to edge energy to find edge step.
> 
> Another option would be to fit predge line and subtract it.  After 
>that,
> fit the post edge normalization range.  
> 
> With Athena, if there is a non-zero slope to the preedge line and 
>you
> choose norm order 1, you get Lisa's result.  With normalization 
>order 2
> or 3, the results should either be the same, or at least, much 
>closer.
> 
> Jeremy
> 

> 
> 
> It is a little hard to evaluate your results, Lisa, without an
> example.  It may help to attach a small project file which
> demonstrates your question.
> 
> Without an actual example, I would have to guess that the bottom 
>line
> is an odd choice of parameters.  This page from the document might 
>be
> helpful:
> 
> http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/bkg/norm.html
> 
> B
> 
> 

> 
> Lisa,
> 
> I think the issue you're seeing is most likely due to telling athena
> to fit the data between E0+199 and E0+200 with a constant.  I'd
> recommend expanding that range some to give Athena a chance -- if
> there isn't any data between E=E0+199 and E0+200, Athena won't be 
>able
> to figure out what the edge step should be.    If you really want 
>the
> edge step to be the value of pre-edge subtracted mu(E) at 
>E=E0+200eV,
> you'll have to do that by hand.
> 
> 
> --Matt
> 
> 
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