[Ifeffit] Questions about fitting of EXAFS

[Bruce Ravel]

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

-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 743, Room 114
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/