Re: [ccp4bb]: pseudo-merohedral twinning

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

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TIMM_DAVID@Lilly.com wrote:
> 
> Hello,  Are there any suggestions for refining structures using
> pseudo-merohedral twinned data?  I have crystals in P21 with a=c,
> beta=95.63 deg, 2-fold NCS, Rmerge = 0.07.  Refinement at 2.4 Ang
> hangs with R-factors ~0.3 using data indexed h,k,l or reindexed
> l,-k,h.  Can index with similar Rmerge in C-centered monoclinic and
> orthorhombic space groups, but does not pack or refine.  Cheers,  Dave
> Timm


 You should check the truncate plots and detwin or one of the other
twinning analysis programs to decide whether it is a perfect twin or
only partially twinned.
 If it is partially twinned with a twinning factor < 0.4 or thereabouts
you can detwin it and do the initial refinement against the detwinned
data.

 Once the structure is reasonably correct you could use eitherCNS or
SHELX I guess to refine against thetwinned data. I have no experience of
this at 2.4A but others may.

 Eleanor