On Thursday 26 August 2004 01:54 am, Peter Southon wrote:
Hello all,
Athena and Artemis do not plot chi beyond 20 Å-1 or the Fourier transform beyond 10 Å. Is this a limitation of Athena/Artemis or of Ifeffit? Can it be changed?
This only seems to be half true. The fe.060 file that comes with the Athena examples has data out to 22 invAng and gets plotted correctly by both programs. On the other hand, you are correct that data only gets plotted in R up to 10 A. That was not a conscious decision by me and seems to be some kind of default in Ifeffit. Matt, how does one change that default?
The 10.5 Å peak raises another issue. I understand that Ifeffit by default assumes that the high-R region is pure noise in order to make its estimates of uncertainty. (I know the actual R-range that is used was mentioned recently but I can't find it in the list archives or any of my manuals.) Can this range be changed? Does anyone have any advice on how to deal with this issue?
In Ifeffit the chi_noise command is used to determine this. Here is its doc page: http://cars9.uchicago.edu/ifeffit/refman/node66.html As you can see, the rwgt1 and rwgt2 parameters are used to change the high-R range. Artemis does not provide widgets for setting these, but you can do this rather more hands-on approach: 1. Open up the Ifeffit buffer from the Edit menu 2. Enter the chi_noise command using the command line at the bottom of that window. To see an example of the chi_noise command, select "What is epsilon_k?" from the Data menu. The chi_noise command used to answer that question (using the default R range) will be displayed in the Ifeffit buffer. 3. The value for epsilon will be diplayed in the Echo area and preserved in the Echo buffer. Enter this number in the box labeled "Epsilon" on the data page. HTH, B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 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/