Dear Friedrich,
There are inequivalent reflections that overlap even in cubic
structures; those where h^2+k^2+l^2 are the same will have identical
d-spacings (e.g. 300 221, 410 322). Check through the list of
reflections to see those that have identical d-spacings; these are also
listed in the Intl. Tables for X-ray Crystallography Vol II (red book) p
125ff. A LeBail refinement will partition the intensity in some way
(probably equally) that is not likely to be what the real ratio is. 2nd
point is name given by SHELX to that R-value, wR2, implies some use of a
weight. The R(F**2) in GSAS is not weighted. Why this all results in a
factor of six; I guess I'm a bit surprised.
Best,
Bob Von Dreele
R.B. Von Dreele
IPNS Division
Argonne National Laboratory
Argonne, IL 60439-4814
-Original Message-
From: Friedrich W. Karau [mailto:[EMAIL PROTECTED]
Sent: Tuesday, October 17, 2006 9:15 AM
To: rietveld_l@ill.fr
Subject: R-Value SHELX/GSAS
Dear colleagues,
may be, that I have comprehension problem. The Bragg R-value is named
R(F**2) in
GSAS and wR2 in SHELX and defined in the same manner.
when I extract the reflexion intesities using a LeBail fit and write
them into a
hklf6 formatted file, SHELX should refine the structure resulting
similar Bragg
R-values like GSAS. The fact is, the the R-values obtained by SHELX are
about 6
times bigger than the R-values obtained by GSAS. The structure is cubic
I, so
that no overlap of the reflections occurs apart from the multiplicity,
that is
incorporated in the hklf6 file. However the structure refines and
converges very
well in both cases. I have testet refinement with both SHELX and GSAS
for a
hexagonal structure, too, but the result is the same. The R-values
obtained by
SHELX are about 6 times bigger than the R-values obtained by GSAS. What
could be
the reason?
Thank you in advance
Friedrich
+ Friedrich W. Karau email: [EMAIL PROTECTED]
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+ AK-Schnick Tel.: (+49) (0)89 - 2180-77449
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