# [Ifeffit] Re: Another Artemis question

Bruce Ravel ravel at phys.washington.edu
Wed Jan 21 13:27:36 CST 2004

```On Wednesday 21 January 2004 01:22 pm, Daniel Carter wrote:
>  How do I constrain the ss (sigma^2) parameter to the Debye Model?  The
> Einstein Model?

Dan,

Let me be a little more explicit this time.

Please go to the web site for the ifeffit mailing list
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit/
and register yourself.  Then ask these questions on the mailing list
rather than of me privately.

There are many good reasons to do so.  One is that you get to hear
from other voices besides mine (although, if you find my prose
irresistable for some strange reason, I do respond regularly to
questions on the list).  Another is that if you ask on a day when I am
on travel (which is often) I may not respond for quite some time.
Finally, your question will probably be of interest to someone else,
as well.

OK, so now that I have vented my spleen, on to your question.

The Debye and Einstein models work very similarly in Ifeffit.

guess theta       = 350
set   temperature = 150 # or whatever temperature in Kelvins you
# measured at

then, later on, in the path definitions, do

sigma2  debye(temperature, theta)

or

sigma2  eins(temperature, theta)

Artemis will tell ifeffit which feffNNNN.dat file corresponds to this
path, so that the geometric components of the Debye and Einstein
models are properly determined from the feffNNNN.dat file.

If you do this for two or more paths, then theta is the variable and
sigma^2 is computed for multiple paths from that single variable.

These two models are neither interchangable nor always appropriate.
You should read what the Feff and Ifeffit manuals have to say about
them.  Some other good references are Ania Poirakova's thesis and PRB,
20:12 (1979) pp. 4908--4911.

B

--
Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
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Naval Research Laboratory                          phone: (1) 202 767 5947
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