[Ifeffit] Plotting chi(k) linear combination fit in energy

Matt Newville newville at cars.uchicago.edu
Mon Jul 20 20:41:57 CDT 2015


I think Ellen wants to first do a linear combination fit with chi(k) data
and then look at what that combination of spectral components  would look
like for the XANES region.  It seems like a fine idea to me.

Off the top of my head I don't know the easiest way to do this.  I don't
think there is a single button for that, but I've been known to miss hidden
features in Athena for years.

--Matt
 On Jul 20, 2015 8:16 PM, "Scott Calvin" <scalvin at sarahlawrence.edu> wrote:

> Hi Ellen,
>
> Either I’m not understanding what you’re trying to do, or what you’re
> trying to do doesn’t make sense.
>
> XANES is generally plotted as mu(E) or norm(E). To get from norm(E) to
> chi(k), two things must be done: a smooth background must be subtracted
> from norm(E), and E has to be converted to k. The conversion from E to k is
> reversible, but the background subtraction is not, since chi(k) is meant to
> be background independent. You therefore cannot, in principle, plot chi(k)
> data as norm(E).
>
> —Scott Calvin
> Sarah Lawrence College
>
> On Jul 20, 2015, at 7:48 PM, Ellen Daugherty <
> ellen.daugherty at colostate.edu> wrote:
>
> Hello,
>
> I was unable to find an example of this question in the archive, but
> please let me know if it has already been addressed. I would like to plot
> the results of linear combination fits performed in chi(k) in energy space
> to compare them to XANES fits. When I try to plot the saved fit in energy,
> I get a message saying: "chi data cannot be plotted in energy." Is there
> any way to do this other than to use Excel to scale the weights of the
> standards? This would be exhausting to perform for combinatorial fits. I am
> using Athena in Demeter 0.9.20 on Windows 7. I have attached a sample and a
> few standards for aid in addressing the issue.
>
> Thank you!
>
> Ellen
>
> --
> Ph.D. Candidate
> Research Assistant, Borch Lab <http://borch.agsci.colostate.edu/>
> Department of Chemistry
> Colorado State University
> http://borch.agsci.colostate.edu/group-members/ellen-daugherty/
> <Sample.nor><Standard 1.nor><Standard 2.nor><Standard 3.nor>
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