[Ifeffit] Exafs distance resolution
Kropf, Arthur Jeremy
kropf at anl.gov
Tue Nov 27 11:02:57 CST 2007
> > This question comes down to the following practical problem. If one
> > has a theoretical model developed using computational
> chemistry that
> > predicts two different bond lengths within one shell, e.g. an
> > octahedral metal center surrounded by 6 oxygen atoms and
> this shell is
> > predicted to be split in three subshells for wich the bond length
> > differs only 0.05 angstroms; and this model can be fit very well in
> > k-space with the splitted shell, off course keeping the
> number of fit
> > parameters below the nyquist criterion. Is there in such a case any
> > physical reason not to fit the experimental data with the splitted
> > shell , but with an averaged 6-atom shell with a larger
> Debye Waller factor?
>
> My guess would be that the EXAFS could probably be fitted
> just as well with one distance and a slightly larger sigma2
> as with 3 separate distances.
> But this would depend some on the data quality and it might
> be right at the resolution limits, so I'd recommend trying
> both models.
>
I think Matt is correct that the fits would be statistically
indistinguishable. However, the paths have just enough distance
difference that using a single shell will probably mess up your
amplitude measurement.
> Cheers,
>
> --Matt
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
Jeremy
Chemical Sciences and Engineering Division
Argonne National Laboratory
Argonne, IL 60439
Ph: 630.252.9398
Fx: 630.252.9917
kropf at anl.gov
More information about the Ifeffit
mailing list