Dear Crystallographers,
I have not done the statistics, but I have noticed that a large portion of
the inquiries directed to the BB are twinning-related. While I recognize
that many of these issues have case-specific details, it may be that there
are references which might address these inquiries in general and therefore
would be helpful to many people here. Could we compile a list, and I will
put the ref's on the wiki?
Regards,
Jacob Keller
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Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: [log in to unmask]
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----- Original Message -----
From: "George M. Sheldrick" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, July 23, 2009 8:41 AM
Subject: Re: [ccp4bb] is my crystal twinned or not?
> It appears that P212121 twinned so that the apparent space
> group is P43212 or P41212 is more common than I had realized.
> This requires that two axes are approximately equal in length
> and that the reflections 00l with l=4n+1 and l=4n+3 are
> 'accidentally' missing. It is possible that in such cases
> translational NCS causes both the twinning and the apparent
> absences, and in addition it can disturb the statistical
> tests for twinning. These problems are likely to be more
> acute when the resolution of the data is relatively low.
>
> George
>
> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry,
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-22582
>
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