I tend to use bond lengths to check refinements. If bond lengths - and
thermal parameters too - aren't physically reasonable, it can mean that the
structure is correct but the refinement is bad, that the structure is
somehow wrong, or the atom assignments are wrong.
Bond-valence sums are great for this purpose. I use Eutax by Mike O'Keeffe
for this, but there are many other programs for bond-valence sums as well.
Philosophically, though, I sometimes get disturbed by the fact that the
structure has to agree with what we already know in order to be published.
It might be better not to think about this too much when doing
crystallography.
- Kurt
-------
Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ 85287-1604
Phone: (480)-965-8853
Fax: (480)-965-2747
-------
-----Original Message-----
From: Jon Wright [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 26, 2004 8:28 AM
To: [EMAIL PROTECTED]
In comparing refinements with different powder datasets there is no
"number of observations" in common usage and no 10:1 rule of thumb.
Broadly, this means "crappy" data with a chemically unreasonable model
can sometimes give much better figures of merit than a good structure
with "good" data.
Sad, isn't it?
Jon
Von Dreele, Robert B. wrote:
>Nandini,
>I suggest you look at the paper "Rietveld refinement guidelines", J. Appl.
Cryst. (1999) 32, 36-50.
>Bob Von Dreele
>
>
>-----Original Message-----
>From: Nandini Devi Radhamonyamma [mailto:[EMAIL PROTECTED]
>Sent: Thu 2/26/2004 8:38 AM
>To: [EMAIL PROTECTED]
>
>Thank you.
>In parallel with single crystal analysis, is there an
>accepted limit for R(F2) or any other parameter like
>Rexp to follow? I'm using synchrotron data.
>nandini
>
>
>
