[Ifeffit] Questions about fitting of EXAFS

[Matthew Marcus]

This point may have come up before in this thread or in one of the numerous links, but I'd like to note that the FEFF version used by default in Artemis usually
requires large E0 for heavy elements like Pt.  Often, the E0 that results in small values of enot is at or above the white line. An easy way to demonstrate this
is to grab a spectrum for Pt or Au foil and fit the first shell.
	mam

On 8/4/2016 8:07 AM, Bruce Ravel wrote:
> On 08/03/2016 05:36 PM, Fuxiang Zhang wrote:
>> Hi, Everyone,
>> I have several detailed questions about EXAFS processing and fitting
>> 1. Are there any physical meaning for DeltaE0 in the paths, why it
>> should be less than 10eV
>
> This paper is a good explanation of why Delta E0 should be reasonably sized:
>
> https://doi.org/10.1107/S0909049598002970
>
>
>> 2. The cutting range of Kmax (FT transform parameters) has great effect
>> on FTs of EXAFS, how do I know to use the best value of Kmax;
>
> If you have measured data with signal well above the level of noise, why would you choose to use less data?
>
> Similarly, if, at some point in your data, the signal becomes dominated by noise -- either statistical or systematic -- why would you include it in the analysis?
>
>
>> 3. How to make refinement equation for multi-scattering paths?
>> Such as in NiFe alloys (simple fcc structure), the path [Ni-FM-3m] Fe1.1
>> Ni1.4 Fe1.1., I use 0.67*Efe+0.33*Eni for DeltaE0, and
>> 0.67*ssFe1+0.33*ssNi4 for sigma2, is that right?
>> Many thanks
>
> Have you been reading the messages posted on this mailing list?  If so, you have certainly noticed that I often answer questions like this one in terms of whether or not a fitting result is "defensible".  For example:
>
> http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg05551.html
> http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg04067.html
> http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg00396.html
>
> and many others.
>
> Make use of the resources at
>
> http://bruceravel.github.io/XAS-Education/
> http://bruceravel.github.io/demeter/
> http://xafs.org/Tutorials
>
> and elsewhere.
>
> Check out Scott's book,
>
> https://www.crcpress.com/XAFS-for-Everyone/Calvin/p/book/9781439878637
>
> or Grant's book
>
> http://www.cambridge.org/us/academic/subjects/physics/condensed-matter-physics-nanoscience-and-mesoscopic-physics/introduction-xafs-practical-guide-x-ray-absorption-fine-structure-spectroscopy?format=HB
>
>
> The library at your university may have either or both of those.
>
> B
>