[Ifeffit] Units for various parameters of ‘feffNNNN.dat’ file

Bruce Ravel bravel at bnl.gov
Tue Feb 28 09:48:13 CST 2017


On 02/28/2017 10:10 AM, Samy Ould-Chikh wrote:
> Dear Ifeffit mailing list,
>
>
>
> I have a question which concern units and I can’t find the answer in the
> Feff manual.
>
> In a FeffNNN.dat output file, what are the unit of the numbers (if any)
> corresponding to
>
> φc,
>
> |Feff|,
>
> φeff,
>
> the reduction factor,
>
> λ,
>
> Re(p)

Samy,

This is a peculiar reference, but I think the clearest written 
explanation of this is in the manual for the ancient "feffit" program. 
Here is a copy of its manual:

http://cars.uchicago.edu/~newville/feffit/feffit.pdf

You will want to look at page 22.  While the rest of the manual is not 
so useful anymore (in the sense that there are very few users of the old 
feffit remaining), it's explanation of how the feffNNNN.dat files are 
used is excellent.

Eq. 6.1 should clarify how each term is used and what the units are. 
Column 1 is, of course, inverse Angstroms.  Columns 2, 3, and 4 are 
unitless.  The two phase terms go into the argument of the sine, thus 
must be unitless.  The amplitude term is multiplied by N and S02, thus 
is also unitless.  The reduction factor, as well, is unitless -- it is 
used in the computation of the amplitude term in equation 6.1.

Lambda has units of angstroms, the real part of p (which is the complex 
wavenumber used in the Feff calculation) has units of inverse Angstrom.

I am pretty certain I got all that right.

I think it would be a good idea to capture all of this information as 
well as eq. 6.1 in the Artemis manual.

HTH,
B


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

  National Institute of Standards and Technology
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