Re: [ccp4bb] is my crystal twinned or not?

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: postdoc position at London, Ontario, Canada
From: Hong Ling hling4 {- at -} UWO {- dot -} CA
Date: 2009-07-23

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Subject: Re: Twinning Reference(s) Addressing Common Twinning Problems
From: Nathaniel Echols nathaniel {- dot -} echols {- at -} GMAIL {- dot -} COM
Date: 2009-07-23

Subject: Re: is my crystal twinned or not?
From: "George M {- dot -} Sheldrick" gsheldr {- at -} SHELX {- dot -} UNI-AC {- dot -} GWDG {- dot -} DE
Date: 2009-07-23

Dear Ulrich,

You are quite correct, I must be getting old and senile!

Best wishes, 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

On Thu, 23 Jul 2009, Baumann Ulrich wrote:

>
> Dear George,
>
> did you mean 4n+2 accidentally missing -- 00l reflections 4n+1 or 4n+3 should
> be systematically absent in P212121 anyway.
>
> Probably I misunderstood something.
>
> Thank a lot,
> Ulrich
>
>
>
>
> Quoting "George M. Sheldrick" :
>
> >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
> >
>
>
>
> --
> ========================================
> Ulrich Baumann
> University of Berne
> ulrich.baumann@ibc.unibe.ch
> phone + 41 31 631 4320/4343
> fax + 41 31 631 4887
>

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: postdoc position at London, Ontario, Canada
From: Hong Ling hling4 {- at -} UWO {- dot -} CA
Date: 2009-07-23

Next message:
Subject: Re: Twinning Reference(s) Addressing Common Twinning Problems
From: Nathaniel Echols nathaniel {- dot -} echols {- at -} GMAIL {- dot -} COM
Date: 2009-07-23