On Friday 24 March 2006 13:01, Scott Calvin wrote:
So here's the question. These three paths are identical except for the identity of one of the scattering atoms. The degeneracy of the path with boron and the path with nickel is the same. Why is the feff amplitude ratio for the boron-containing path higher than that of the nickel-containing path? Shouldn't nickel scatter more strongly? And yes, I double-checked...the potentials are defined correctly in the feff.inp file.
Scott, I am inclined to side with Jeremy and Feng. One might be surprised by how quick-n-dirty the amplitude calculation is. If memory serves (and who knows how likely *that* is), feff computes the complex chi(k) using plane waves, which is a very quick calculation. It then adds up the magnitude of the complex chi(k) at 4 points. That's it. The amplitude is never meant to be more than a guide to eye. As you well know, to know how each path contributes to the data, you actually need to plot them or -- better -- do a fit. 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/