Thank you for all the quick reply. Here are the additional information
about the crystal. The crystal was frozen and shot in synchrotron. The
collection was 1degree/frame. The space group and unit cell are P21
and a=70 b=165 c=170 alpha=90 beta=90.1 gamma=90. I processed the
data in P1 first (I did not see any abnormal changes during
integration), and then merge them using P21 or P2221. P21 gives
reasonable Rmerge of ~10% while P2221 has much higher Rmerge of ~30%.
I reprocessed the data with mosflm using P1. And Pointless also
suggested the space group of P21.
Zhiyi
On 1/5/12, Jens Kaiser <[log in to unmask]> wrote:
> What are your cell constants and space group? It sounds to me you
> misindexed and then artificially "twinned" your structure by
> integrating/merging in too high of a symmetry. I've seen that happen for
> primitive hexagonal which was actually C-centered monoclinic.
> Also, in my experience this is more likely to happen with
> denzo/scalepack as it refines every image and does postrefinement in
> scalepack. XDS will decide for you on a symmetry after integration, and
> in MOSFLM you should see earlier that something is wrong.
>
> HTH
>
> Jens
>
>
> On Wed, 2012-01-04 at 21:42 +0800, Zhiyi Wei wrote:
>> Dear all,
>>
>> I recently collected a dataset (~2000 frames) from a single crystal.
>> If merge first 600 frames (sca1) or last 600 frames (sca2), Rmerge
>> values from scalepack seem to be ok (~10%) though rejection ratios are
>> high (~5%). But if I merge all frames together, Rmerge value goes up
>> to ~20% and rejection is extremely high (~20%). Then, I checked sca1
>> and sca2 by xtriage in phenix. Surprisingly, the logfiles told me that
>> sca1 is no twining while sca2 is very likely to be twinned. I never
>> met this case before. So, I am wondering if it is possible from a
>> non-twinned structure to a twinned structure just due to radiation
>> damage. If the answer is yes, does it mean that I should not collect a
>> large number of frames to amplify anomalous signals by using this
>> crystal?
>>
>> Thanks a lot!
>>
>> Best,
>> Zhiyi
>
>
>
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