Abhijeet, Consider the energy resolution of the dispersive EXAFS beamline. A poor energy resolution could suppress the low-k amplitude causing the Debye-Waller factor to compensate by being articifically low. However, you also have an amplitude larger than 1. Adding an Ei component will address the problem of poor energy resolution, but I would suggest that it should be based on the measured energy resolution rather than being a "guessed" variable. You can also measure the appropriate Ei using a known sample, such as a copper foil for which you have comparable spectra on a beamline with better energy resolution. What scattering paths and at what bond lengths are responsible for the peak below 1 angstrom? It seems unlikely to me that a Cu-O or Cu-N path would produce such a peak. These peaks would more typically be closer to 1.5 angstroms. Jeremy Kropf Chemical Sciences and Engineering Division Argonne National Laboratory Argonne, IL ________________________________ From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Abhijeet Gaur Sent: Wednesday, July 14, 2010 2:00 AM To: ifeffit Subject: [Ifeffit] Negative ss problem Hi all, I read the discussion on negative Debye waller factor. As per the discussion the negative value of this factor shows that the model has shortcomings, so it should be corrected. I am also getting the same problem while fitting one of my samples. It is a Cu complex whose EXAFS data is taken at Dispersive EXAFS beamline at RRCAT, Indore, India. In the complex the nearest neighbours of Copper atom are Nitrogen and Oxygen. I am getting a very good fit upto 3rd shell but the problem is that all ss parameters are coming negative. I checked the model it seem correct. Also I am getting a peak below 1 Angs which is also getting fitted but I am not able to get that whether it is a real or due to some noise. I am attaching herewith the results of data analysis and fitting. Thanks in advance With regards Abhijeet Gaur Vikram University Ujjain, INDIA