Re: [ccp4bb]: twinning detection

[Wim Burmeister <wpb@embl-grenoble.fr>]

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There must me something seriously wrong with your data.
-  Either you think that you are using F's but in reality you are using I's
-  Due to the presence of ice or salt you have measurements which have aberantly high
intensities
-  Your spacegroup is incorrect and does not take into account systematic absences for
which you measured reflections which are not really there. A simililar problem could
arise if you get some pseudo-symmetry corresponding to a centered lattice. In this
case many of the reflections will be very weak.


Greetings

Wim

Zhang Fan wrote:

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>
> Dear all,
>
>         I suspected that my data is twinned and carried out the twinning detection
> using the input file detect_twinning.inp in CNS. I got the following
> result:
>
> ---------------------------averages-over-all-bins-----------------------------
>
>    <|I|^2>/(<|I|>)^2 =    4.0639 (2.0   for untwinned, 1.5   for twinned)
>   (<|F|>)^2/<|F|^2>  =    0.5682 (0.785 for untwinned, 0.865 for twinned)
> ------------------------------------------------------------------------------
>
> Why the statistics of my data is so far away from the idea values for
> either twinned or untwinned data. Is my data twinned or not from this
> result?
>
> Thanks in advance.
>
> Fan
>
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Wim Burmeister                    Maitre de Conference
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