Hi Dr. Newville,
I had similar situation and questions as with choosing Path Parameters. My goal is to identify the occupancy sites for a doped element in my sample. We have a rough guess of two possible sites, part of the doped atoms are filling a void site of the unit cell, the other part is to substitute an existing atom sites.
I was being able to writing two ATOM files and run FEFF twice to calculate all possible PATH. But when I was going to define/guess the parameters ('N','amp', 'enot', 'delr','ss')for EACH path, I totally lost idea how to group all those paths, or how to guess all those five parameters for each path. Of course, I couldn't get a good fit as I don't know how to build the model and to refine parameters in this step.
Here I post my understanding of the five parameters: 'N', path degeneracy, or coordination number; 'amp', usually close to 1, but as I have doping elements, I am expecting small partial numbers in some of the 'amp' to adjust for partial occupancy; 'enot', I think it is just the energy shift of your spectra, and as I believe my spectra are well aligned, I will SET 'enot' to zero. 'delr' is the variation of the real atom-atom distances from the calculated ones (I think I need to group paths to refine 'delr' but I don't know what's the criteria to group paths). 'ss' is to consider about the disorder effect and typically I use the Debye model. Let me know if I am wrong in any way.
Could you please give me some suggestion how did you get started? I am looking forward to hearing from you.