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

[Samy Ould-Chikh]

Thanks Bruce.

Indeed having the real equation that Artemis is manipulating would be great for recent version too.

I am a bit surprised about φc and φeff.
I was expecting radian unit...


Best Regards,
Samy Ould-Chikh

KAUST Catalysis Center
Bldg.3,Level 4, #4231
4700 King Abdullah University of Science & Technology
Thuwal 23955-6900
Kingdom of Saudi Arabia

Tel: +966 12 8084486
E-mail: samy.ouldchikh at kaust.edu.sa
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-----Original Message-----
From: Ifeffit [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Bruce Ravel
Sent: Tuesday, February 28, 2017 6:48 PM
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Units for various parameters of ‘feffNNNN.dat’ file


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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