[phenixbb] pseudo-merohedral twinning or pseudo-symmetry?

[Francis E Reyes]

Is there a model available? How much of it is built/homologous? You  
should try indexing it with labelit (try several images) and see if  
P222 is still the proper point group.


See http://cci.lbl.gov/~phzwart/p222.png for subgroups under p222. You  
may need to consider the lower P2 space groups for this problem.


FR
On Oct 16, 2009, at 1:20 PM, Laurie Betts wrote:

> Hi - We have a data set that seems to process well in primitive
> orthorhombic.  a=80, b=87, c=114.  The data  has overall Rsymm around
> 10% to 2.6 Angstrom, where I/sigI > 2, and Chi-squared is around 1.4.
> Phenix.xtriage shows some pathology in intensity statistics such that
> the L-test indicates <|L|> = 0.414 and <L^2> = 0.241, with the L-test
> Z score = 7.334.  The Wilson ratio for acentric refls is 1.774.
> According the xtriage, There were no "pseudomerohedral" twin laws
> found, and the comments at the end say "As there are no twin laws
> possible given the crystal symmetry, there could be a number of
> reasons......"
>
> Is it more likely that this is a case of pseudo-symmetry, or would one
> not expect the intensity statistics to have the values they do in that
> case.
>
> Also, is the absence of twin laws defined by the fact that proper
> merohedral twinning is not possible for P222 space groups?
>
> Still confused,
>
> Laurie Betts
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---------------------------------------------
Francis Reyes M.Sc.
215 UCB
University of Colorado at Boulder

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