Thank you all for the answers. The Kmax effect on the shape of magnitude of FTs of one of my samples may come from the low signal/noise ratio. I still not sure if there's any physical meaning of DeltaE0, Does it relate to the shift of absorption edge?
Fuxiang On Thu, Aug 4, 2016 at 1:35 PM, Scott Calvin <dr.scott.cal...@gmail.com> wrote: > I’ll add to Bruce’s comment that if the choice of kmax has a great effect > on the parameters found by the fit, that’s an indication of a problem! Good > fits should be stable to modest changes in kmax (e.g., an inverse angstrom > or two one way or another). The statistics may suggest one kmax or another > is somewhat better, but the fitted parameters should not be drifting > outside of the ranges defined by their uncertainties. If they are, you have > an unstable fit. In that case, there are several possibilities: perhaps you > are including an artifact in your k-range (e.g. the beginning of another > edge) or a lot of data dominated by noise. Or perhaps your model is having > trouble distinguishing between two fitting minima, and is flipping back and > forth between them (this is more likely if your fitting model is fairly > complicated, with many free parameters). In any case, if you’re fit is > highly sensitive to kmax you should investigate to try to determine why. > > —Scott Calvin > Sarah Lawrence College > > > On Aug 4, 2016, at 11:07 AM, Bruce Ravel <bra...@bnl.gov> wrote: > > > >> > >> 2. The cutting range of Kmax (FT transform parameters) has great effect > >> on FTs of EXAFS, how do I know to use the best value of Kmax; > > > > If you have measured data with signal well above the level of noise, why > would you choose to use less data? > > > > Similarly, if, at some point in your data, the signal becomes dominated > by noise -- either statistical or systematic -- why would you include it in > the analysis? > > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit >
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