Re: [ccp4bb]: averaging with centred space groups

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

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Jan Abendroth wrote:
> 
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> Dear crystallographers,
> I think to remember that non-crystallographic averaging during density
> modification is less powerful in (c)-centred space groups than in
> others.
> 
> Is this true or complete nonsense?
> Could anyone give me a reference for this?
> I can't find it any longer.
> 
> Thanks in advance and regards
> Jan
> --


 I cant see why?
All averaging is less powerful if the operator does not sample different
points in reciprocal space; ie a pseudo translation is more or less
useless; a rotation which is parallel to a reciprocal crystallographic
axis is less useful than one in a totally general position. 
In my experience NCS in monoclinic space groups is often about an axis
in the a-c plane so falls into this category. But that is simply
anecdotal - Kevin cowtan has done some exploration of this and discussed
it at the IUCr meeting in glasgow - Email him and ask if he published it
anywhere ( cowtan@ysbl.york.ac.uk)

 Eleanor