Hi Matthew,
This may be a minor (and possibly different) point, but vibrational
broadening can be different for different pre-edge peaks. See for example,
Keith Gilmore and Eric L Shirley 2010 *J. Phys.: Condens. Matter* *22*315901.
Cheers,
Josh Kas
On Mon, Oct 10, 2011 at 11:42 AM, wrote: Send Ifeffit mailing list submissions to
ifeffit@millenia.cars.aps.anl.gov To subscribe or unsubscribe via the World Wide Web, visit
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
or, via email, send a message with subject or body 'help' to
ifeffit-request@millenia.cars.aps.anl.gov You can reach the person managing the list at
ifeffit-owner@millenia.cars.aps.anl.gov When replying, please edit your Subject line so it is more specific
than "Re: Contents of Ifeffit digest..." Today's Topics: 1. Re: number of independent points (George Sterbinsky)
2. Re: lifetime broadening of pre-edge peaks? (Matthew Marcus)
3. Re: lifetime broadening of pre-edge peaks? (Anatoly I Frenkel) ---------------------------------------------------------------------- Message: 1
Date: Mon, 10 Oct 2011 14:04:07 -0400
From: George Sterbinsky Content-Type: text/plain; charset="iso-8859-1" Bruce, Matt, and Jeremy, Thank you for explaining this. Your responses are much appreciated. George On Mon, Oct 10, 2011 at 11:35 AM, Bruce Ravel On Monday, October 10, 2011 10:35:12 am George Sterbinsky wrote: Since I haven't received a response to my previous question, I just
wanted
to make sure I asked it clearly. I suspect the lack of response had more to do with it being a
non-trivial question asked on a Friday afternoon :) To elaborate, I am attaching a log from
Athena. The log file lists: "Independent points = 27.057617188" If I attempt to reproduce this result using the equation in the feffit
document, I find Nidp = { [2*(kmax - kmin)*(Rmax-Rmin) / pi] + 2} = { [2*(14 - 0.5)*(4.2 1.0) / pi] + 2} = 29.50197417, where I have used the k-range and R-range in the log file as kmax,
kmin,
Rmax, and Rmin. Can someone explain to me why may calculation does not reproduce the
number
given for "independent points" in the log fie? George, A quick examination of the ifeffit source code shows that there are
two issues: 1. Regardless of what it may say in the document, Ifeffit uses "+0"
rather than "+2". See line 345 of
http://cars9.uchicago.edu/svn/ifeffit/trunk/src/lib/iff_feffit.f A bit of history: Ed Stern wrote this paper back in 1993:
http://dx.doi.org/10.1103/PhysRevB.48.9825 Over the years, many have expressed scepticism of his conclusion.
The Bayesian work I mentioned earlier suggests quibbling over the
value of N in the "+N" term misses the bigger issue. Ifeffit's
use of "+0" provides a conservative yet easily stated estimate of
Nidp. 2. The difference to the left of the decimal point has to do with the
fact that Artemis allows you to pick any value for kmin, kmax,
rmin, and rmax. When Ifeffit evaluates Nidp (and anything else)
is actually takes the nearest grid points to those four values.
The grid in k-space is 0.05 inv. Angstroms. This sets the grid in
R space to be about 0.03 Angstroms, but not exactly. So the
values of Rmax and Rmin used by Ifeffit to compute Nidp (and other
things) are not quite what you specified. At some point, George, you may want to bite the bullet and look at
source code. Details are not unknowable, they just might not be
written down anywhere beside the source code. Here is the top of Ifeffit:
http://cars9.uchicago.edu/svn/ifeffit/trunk/ B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology
Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
Building 535A
Upton NY, 11973 My homepage: http://xafs.org/BruceRavel
EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter
_______________________________________________
Ifeffit mailing list
Ifeffit@millenia.cars.aps.anl.gov
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit