Re: [ccp4bb]: Please teach about twinning

["Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>]

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Kunchithapadam Swaminathan wrote:
> 
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> 
> Dear :
> 
> In connection with the twinning discussion, I am open to admit that many of
> us are in the situation:
> 
> Everything you wanted to know about twinning but afraid to ask
> 
> Can some experienced and kind soul (including the program authors) post a
> mini tutorial, with protocols, pointers and computer program steps, for:
> 
> 1.  Symptoms of twinning (and details of the buzz words like twin factor,
> merohedral and hemihedral twinning)
> 2.  Data collection, reduction and correction
> 3.  Structure determination and refinement
> 
> Obviously, there is a fear if you realize that a crystal is twinned and
> immediately we just throw the crystal away or pretend to do something, which
> leads to nowhere.
> 
> With regards,
> Swami

 Maria Turkenburg and I put together something for CCP4 - it is on the
documentation part
GENERAl 
twinning

 At least it gives symptoms of twinning
 Possible twin operators

 twin factor ( ratio of the volumes of the two overlapping crystals)

 merohedral and hemihedral twinning

George Sheldrick and Regine Hersbst X have definitions in the SHelx 97
manual

There is material on Tom Yeates web site
http://www.doe-mbi.ucla.edu/Services/Twinning/

Eleanor