On Sunday 13 April 2003 03:06 pm, Matt Newville wrote:
This will do only the central-atom portion of the phase-shift, so will be incomplete, but is often most of the correction, will work for the whole spectra, and doesn't require knowing much about the system. Athena (the excellent GUI to ifeffit from Bruce Ravel) can do these central-atom phase-corrections very easily (ie, no typing commands).
Hi, I just wanted to quickly chime in on this topic. For what it's worth -- I am not a huge fan of phase corrections. While they do, in many cases, make the chi(R) look more like a radial distribution function, they do require some more explanation when showing your data to a non-xafs person. And, while a pc-chi(R) looks more like the corresponding RDF, it most certainly is not an RDF. Athena does only a central atom correction for the reason that Matt gave. Athena assumes only that your data is XAFS data and does not assume any knowledge of the system. Thus, the only thing that Athena is sure to know is what the absorbing atom is. That is determined from the edge energy. Artemis, on the other hand, has more information to work with. When you choose to do phase corrections in Artemis, you choose one of the feffNNNN.dat files included in the fit as the phase correction standard. Thus, in Artemis, phase correction includes the scattering portion as well as the central atom portion. In this screenshot: http://leonardo.phys.washington.edu/~ravel/software/exafs/images/artemis/art... the "Path to use for phase corrections" menu consists of "None" (i.e. no pc), and each of feff0001.dat through feff0005.dat. You might then choose to use feff0001.dat (i.e. the first shell in the example shown) for phase corrections. Note that the corrections are only for plotting. Fitting in artemis is done with the non-phase-corrected data and theory. Upcoming news flash: I have spent the last week getting multiple data set fits working in Artemis. Ifeffit has supported them for a long time, but now Artemis will provide an interface to that extremely useful tool. I hope to have the new release out soon. 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, X24c, U4b 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/