[GSAS-II] Single peak fits

[Von Dreele, Robert B.]

Dear Davide,
Actually what happened is that if sig & gam are not refined, they revert to what would be calculated from U, V, W X & Y. Usually one refines X & Y during single peak fits & not sig or gam. This assumes that U, V & W have been established for the diffractometer so sig is fixed by them, and that the sample broadening (almost always Lorentzian) is isotropic and thus given by X (related to size broadening) and Y (related to mustrain broadening). If the broadening isn't isotropic, the usual approach is to refine X & Y and any individual peak gam that seem to be anomalous (usually a handful). NB: this usually has little or no effect on peak positions needed for e.g. indexing.
Bob
Hi,
When I refine the peaks with the peak fitting routine I found a problem: if I refine the sigma and gamma peak parameters and then I fix the gamma parameters these parameters become 0 after the fitting.
I think it is a bug in the code.
bests
Davide



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