[Ifeffit] Can the degeneracy (N) in Artemis be a variable?

[Carlo Segre]

Hi Peng:

The answer is yes, you can use a variable called "n" or n_o" but you need 
to be careful on how you set up the fitting.  here is one way to do it:

For the path of interest, in the two boxes which are labeled "N" and 
"S02", you fill them in as  "1" and "n_o" (for number of oxygens for 
example).  Then you let "n_o" (note that at least in Artemis, lower case 
is the same as upper case in variables) vary as a guess parameter.  The 
result will be a number that is of the order of the number of near 
neighbors but it will be too large by the factor of one over the amplitude 
reduction factor.  If you have a way to estimate the amplitude reduction 
factor as a set variable called "amp" you can set up the model a bit 
differently, putting "amp * n_o" in the "S02" box.  This might give a 
better estimate of the coordination number (path degeneracy).

Note that numerically there is no difference between the above and taking 
a guessed value of "amp" and multiplying it by the number in the "N" box. 
It is simply a matter of convenience and ease of looking at the output.

Carlo

On Sat, 26 Jul 2014, Peng Liu wrote:

> Hi all,
>
> When I model a standard, I know the degeneracy through the other data. But 
> for spectra of unknown material, I would like to set degeneracy as a variable 
> like the amplitude, deltE0, e.g.. However, I can assign a letter to N and 
> define it. Do you have any idea how I should do it?
>
> Thanks for your reply,
>
> Peng
>
>

-- 
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org