>So who invented first the "total Rp and Rwp" ?? This don't seems to
>be H.M. Rietveld, IMHO.
As I said earlier, it seems to have been introduced in the early
versions of the DBWS program; for the same data and the same
structure parameters, this resulted in lower R-factors.
Including the background in the refinement and R-factors is not wrong
en principe. It is just that some users naively believe that a low
R-factor implies a good structure :-) But you can also obtain a low
R-factor, without having a good structure, by fitting low resolution
data, or data that is not sensitive to some of the structure parameters
(eg light atom positions with X-ray data).
Hugo Rietveld didn't include the background in the definition of the
profile R-factors, and that choice IMHO appears to be the best. He did
correctly include the background in calulating the statistical error for
each point (the weighting scheme), and he did correctly calculate the
estimated errors in the parameters. That is much more important than
simply obtaining "low R-factors".
>The problem is that some softwares give only
>these meaningless total Rp and Rwp so that their users have no way
>to access to the conventional R values (if you want a list of these
>softwares, let me know)
Go ahead Armel, reveal all :-)
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/