[Ifeffit] Amorphous

Bruce Ravel bravel at bnl.gov
Mon Aug 8 10:35:04 CDT 2016

On 08/08/2016 11:19 AM, Carlos Triana Estupinan wrote:
> I want to know if it is possible to obtain a 3D structure (.cif file) of
> an amorphous material from the EXAFS fitting carried out from artemis. I
> mean, there is a way to extract a .cif file with the structural data
> obtained from the refined spectra.


EXAFS is basically a one-dimensional measurement.  You measure R. 
Multiple scattering gives you limited information about the 3D 
arrangement of atoms, but mostly EXAFS is just R.

Unless I am misunderstanding the question, I don't think you can do what 
you are asking even for a well-ordered crystal, much less an amorphous 

> Also, in amorphous materials there
> must be a distribution of interatomic bond distances and coordination,
> and so, how can I address such a structural distribitions.

Well, sure.

There is a while literature on the use X-ray or neutron scattering along 
with EXAFS and molecular dynamics and monte carlo methods to study 
amorphous materials.  It seems that the most successful approaches 
involve forward modeling -- i.e. testing structures against the EXAFS data.

There simply isn't enough information in EXAFS to invert the EXAFS and 
extract a 3d configuration.  Artemis does not even try to do that.


  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/
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  Demeter:     http://bruceravel.github.io/demeter/

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