On 12 Aug 97 at 11:48, Armel Le Bail wrote:
> At 10:26 11/08/1997 -0600, Bob Vob Dreele wrote:
>
> >In case any one was wondering...
> >>Then, if I am not wrong, I have one question : who invented the
> >>total Rp and Rwp factors ?-) I suspect that they were invented
> >>by error or just for an endless discussion about their absence of
> >>meaning regarding the crystal structure...
>
> Yes Bob, sure that Rp and Rwp were originally described by Hugo
> Rietveld.
>
> But.
>
> Remember that the background was not originally described by
> functions with refinable parameters. So that the function practically
> minimized (i.e. in the original softwares) was not including the
> background. And this was logical.
>
> Have a look at fig. 4 in J. Appl. Cryst. 2 (1969) 65-71 by H.M.
> Rietveld and observe the zero background, a fact which is
> certainly not experimental for CaUO4 on any neutron diffractometer.
> So that, even if this is not explicitly written in the paper, the yi(obs)
> in the Rp formula is in fact Iobs-background. Remember the first
> versions were in two steps, one for preparing data and one for
> the refinement. The background was subtracted in the first step
> (or am I wrong ??). This background corresponded to values
> interpolated between intensities estimated manually at a few
> angular values.
>
I just want to confirm Armel Le Bail's remarks about the background
corrected intensities in H. M. Rietveld's original paper in J. Appl.
Cryst. 2 (1969), 65-71. It is not only obvious from the plotted patterns
in Fig. 4 and 5 in addition Hugo Rietveld wrote explicitly in his
paper in the Section: Experimental about the background corrected
intensities yi in the form:
yi = Yi - Bi, where Yi is the total intensity at step i and Bi is the
estimated background as described above and in the paper. The
equation dealing with the calculation of Rp uses only the corrected
yi values.
The easiest way to proof is the original paper by Rietveld which you
can read without leaving your desk by browsing through the WWW to
Hugo Rietveld's own homepage at: http://home.pi.net/~rietvld/home.html
or to the location of the paper at: http://chemsg7.tau.ac.il/xtal/paper2/paper2.html
> So who invented first the "total Rp and Rwp" ?? This don't seems to
> be H.M. Rietveld, IMHO. Or maybe the old software I just had a
> look inside was not the original ?
>
Its an interesting question for me too.
Jens Trommer