[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
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/
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