[Ifeffit] Athena (linear combination fitting)

Bruce Ravel bravel at bnl.gov
Thu May 12 10:12:22 CDT 2011

On Thursday, May 12, 2011 10:11:20 am Matt Newville wrote:
> Linear combinations fits are more challenging for EXAFS
> than for XANES, as EXAFS are complicated by disorder terms that do not
> strongly effect XANES, and this disorder is a "component" of the data.
>   Unless you understand the set of possible atomic environments very
> well and are only interested in the fractions of known phases, I'd
> recommend against using simple linear combinations of EXAFS for
> anything except exploratory analysis.

I certanly didn't make this point strongly enough.  I too am wary of
chi(k) LCF fits in most situations.

A common example of the disorder problem is a system that forms metal
nanoparticles.  Using bulk metal as a standard in the XANES LCF is
much less wrong than using bulk metal as a standard in chi(k) LCF.



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

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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