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Re: [ccp4bb]: indexing
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Manfred Buehner wrote:
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> On Wed, 19 Apr 2000, Quan Hao wrote:
> > We have collected some data on station F1 at CHESS. The crystals appeared to
> > be hexagonal thin plates and diffracted to about 2.2A. We collected 75
> > degrees of data for each of the three crystals. The spot shapes looked OK
> > but we could not index the spots using DPS, DENZO or MOSFILM. The spots
> > seemed to align along straight lines on all images and one could see the
> > hexagonal features. Has anyone come across this before? Your help is greatly
> Think of twinning! Think of pseudo-crystalline aggregates!
Twinning usually does not prevent indexing in those spacegroups where
the lattices overelap precisely. It will stop you solving the structure
but most indexing programs are only interested in picking up spot
positions whjich are just the same for perfectly twinned crystals. If
you have one of the weirder monoclinic forms where the twinning involves
a* aligning with a*+2c* then you get some rows apparently twice as
populated as others. But again the indexing usually gives a result.
Surely the autoindexing at least gives a P1 cell?