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Re: [ccp4bb]: Non-merohedral twinning



Dear Roeland,

In case of a non-merohedral twin the reflection do not overlap perfectly.
The only way is to untwin the data with the reduction software.
And refine against the untwinned data.

I can see basically two reasons, why Your Rmerge is that high.

1: You included partially overlapping spots.

Unless there is (as I know) no working algorithm that integrates partially overlapping spots
on the marked.
You have to reject them. If your completeness decrease to much You can try
to get these reflections from the other domain.

2: The software is not able to determine the position of partially overlapping spots
correctly. This leads to an insatiable refinement.

Check whether or weather not some of Your parameters are "running" away.
(orientation, distance, cell, ....) If yes fix them. Play with spot- and box-size.

b.t.w.  such a structure will never be of the same quality as an single crystal.
The best solution is to try to get single crystals.
Or if You have surgeon skills try to cut Your crystals.

All the best
(:hristopher
 
 

Roeland Boer wrote:

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Hi there,

I'm working on a dataset from a sample that is non-merohedrally twinned.
I got the twinning operation and can process the reflections of the
major component of the twin, but got a rather high Rint (11%). I thought
that the two lattices would not overlap too much, but apparently they
do. I'd like to detwin the data, and was wondering if somebody can point
out programs that can handle NON-merohedral twinned data.

Thanks a lot,
Roeland.

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