Re: [ccp4bb]: orthorhombic twinning

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

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Daniele de Sanctis wrote:
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> 
> I already checked if the space group were tetragonal, but the R-merge
> value suggest me that it wasn't.
> Giving a look at the cumulative intensity distribution, it doesn't seem
> to be "sigmoidal" and the |E^2-1| statistics are higher (and not lower)
> than the expected value, and I really don't know how to interpretate
> that result! thank you all for the help!


  What about the 2nd moment - my personal favorite..

  But you must also check the native patterson - do a 4A patterson and 
see if there is a pseudo translation indicated by an off-origin peak 
which is a substantial ( > 20%?) of the origin..

  If so the intensity statistics are suspicious anyway..
E

> 
> daniele
> 
> 
> 
> 
> 
> 
> "F.Xavier Gomis-Rüth" wrote:
> 
>>Caro Daniele,
>>just that two axes are very close to each other (even identical) does
>>not necessarily mean that
>>something is wrong. We just had a case that was exactly the same: two
>>cell parameters were
>>(almost ? probably certainly ?) equal, so you could index the data with
>>P4. However, when
>>scaling, something was clearly weird: scala threw away too much data and
>>the Rmerge, despite
>>not being really bad, was suspicious.
>>When indexing, integrating and scaling as orthorhmobic (it finally
>>resulted in being, as in your
>>case, precisly P212121) everything went fine.
>>Something different is if your molecule doesn´t fit into a P212121 cell...
>>Could you give more infos ?
>>Sorte !
>>Xavier
>>
>>daniele@ge.infm.it wrote:
>>
>>
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>>>
>>>
>>>dear all,
>>>i have a crystal with orthorhombic space group (P212121) with two cell
>>>dimensions lenght very similar, so i think that the crystal is twinned.
>>>So, what can i do now? is there a software to detwin my data also in this
>>>particular case?  There something else that i should try (except to search
>>>for different crystallization conditions?)?  thank you
>>>
>>>
>>>daniele
>>>
>>>
>>>
>>>
>>>
>>>
>>
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>>                 *               F.X. Gomis-Rueth                *
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>