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@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/
On Wednesday 21 January 2004 04:05 pm, Tamas Varga wrote:
1. What's the exact definition of the R-factor used to evaluate the fractional misfit?
Read Chapter 5 of this document: http://cars9.uchicago.edu/feffit/feffit.ps It's the old feffit manual, but the definitions of chi-square and R-factor are the same.
2. Can Artemis fit just Fourier filtered raw data in k-space?
If I understand your question, then, yes. On the data page in Artemis there is a drop-down menu labeled "Fitting space". One of the options is "q". In ifeffit-speak "q-space" means "Fourier filtered k-space". We had to call it something.... ;-) If I recall correctly, the back transform will be done over the R-range and the fit will be done over the k-range of the original FT. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/
participants (2)
-
Bruce Ravel -
Tamas Varga