[Ifeffit] lambda in parameter Ei

[Bruce Ravel]

On Saturday 13 May 2006 17:20, Arkadiusz Onyszko wrote:
> Dear All,
> I found in manual, that lamda ~ 1/sqrt(Ei)
> I want calculate lambda with fitting parameter Ei. How do it ?
> What is the exact dependence Ei and lambda ?
> During fitting I have example Ei=7,5, so I want calculate lambda.
> This dependence: lamda ~ 1/sqrt(Ei) is not a complitly.

When fitting with Ifeffit, Ei is a correction to the broadening terms in Feff,
one of which is the mean free path.  The exact effect of Ei on the exafs
equation as used in Feff and Ifeffit is explained in chapter 6 of this
document: 
  http://cars.uchicago.edu/~newville/feffit/feffit.ps

Asyou can see from equation 6.2, Ei is actually a correction to the complex
momentum.  The complex momentum is related to the mean free path, but also to
other things in Feff's energy model.  This makes the precise interpretation of
Ei rather subjective.

Is Ei a correction to Feff's loss terms?  Is it a correction to Feff's value
of the mean free path?  Both?  Apparently, you are hoping that you can
interpret Ei entirely as a correction to the mean free path.  I'm not sure how
you know that, but if so, Eq. 6.2 tells you how to do so.  (And don't forget
the constants -- 2m_e/hbar^2!)

Hope that helps,
B



-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

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