On Monday, August 01, 2011 12:36:19 am Nicholas.Tse@csiro.au wrote:
Just wondering what could I do to make the amp guess value as a positive number? If I run it and let it float (i.e. guess), the amp becomes negative in the resulting fits, but the fit has nice delr and ss values (i.e. make sense). If I restrict the amp value to 1, everything else doesn't fit. I am only fitting the first nearest neighbour in a measured standard; Gadolinium oxide.
Are you sure that you ran the Feff calculation with the correct edge? You will find that the K edge and L3 edge calculations are roughly 180 degrees out of phase. That mistake (one I make annoyingly regularly) could account for a negative amplitude. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/