>Potentially silly queries.
>Are there any newish references around the place about the
>validity of R Bragg in Rietveld analysis.
R-Bragg is of course not minimised in Rietveld refinement,
and is only an indication of the fit, for users more familiar
with single crystal refinements.
>Also, when using capilliary data from such machines as an
>INEL PSD. You can get quite nice Bragg R's purely becuase
>20% to 80% of the intensity that is being fitted relates to
>the background. Thus are there any background subtracted
>versions for Rietveld of Bragg R referenced in the literature?
It was true that some profile-R's defined to include the fit to
the background eg in the DBW program, gave spuriously low
values for this kind of reason - especially low R's for high
B/G's :-) but Bragg-R refers to integrated line intensities,
and should not be affected in the same way. And why should
it be any different for INEL PSD data ?
Low R-factors can also be obtained with low resolution or
truncated data, which can be fitted very well without
necessarily resulting in a good structure.
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Alan.
Alan Hewat, ILL Grenoble, FRANCE <hewat@ill.fr> tel (33) 4.76.20.72.13
ftp://ftp.ill.fr/pub/dif fax (33) 4.76.48.39.06 http://www.ill.fr/dif/