On Wednesday 07 March 2007 22:19, David Weedon wrote:
The parameter "amp" is defined as the relative importance of the path and is assigned a value eg. 100 or 30, is this some form of percentage of this path to the first (major) path?
That's correct. When Feff computes the contributions from each path, it does a very quick and dirty approximation of the amplitude of that contribution. Typically, but not always, the amplitude of the first path is the largest, so it gets an amplitude factor as reported by Feff of 100. Each subsequent path gets the same quick 'n' dirty approximation of size, which is reported as a percentage of the rough size of the largest path. The point of all that is to give you, the user, a sense of which paths will contribute significantly to the EXAFS. But it's just a guide to the eye. That amplitude approximation doesn't include sigma^2 or any modifications to coordination numbers that you might find in your actual data. Sometimes paths that are reported as big paths turn out to be very small contributions to the fit. Also sometimes, the small-ish paths turn out to be measurable in a fit. It's just a guide to the eye. B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/