Hi Yu-Chuan, I have not looked at the project file, but I have a few comments anyway:
I attached the apj file of magnesium orthovanadate. If you change the k-range, says, from 4~10 to 3~10. The fitting results will vary. Or you can change other stuffs. Somtimes the results are consistantly, somtimes not.
If you change the k range (or other FT parameters), the fitting results can definitely change. How much the results change for small changes in FT parameters is a good indication of the reliability of the fit results. Of course, saying that the results change needs to include not only the best-fit values, but also the uncertainties.
By the way, I wonder if my first sell DW factor is about -0.0001 and the uncertainties is +/-0.0015. Can I say that it is possible for positive DW factor for my first sell fitting? Thus, my fitting is reasonable?
Well, -0.0001 +/- 0.0015 is consistent with zero. This is also a very small absolute value for sigma2. At k=10, the Debye-Waller factor, exp(-2*k*k*sigma2) = 1.02 for sigma2=-0.0001. There are many ways to get a 2% error in amplitude. One possibility (there are many) for why you could get a sigma2 that's smaller than "it should be" is that the fitting model puts in more static disorder than is really there. --Matt