[phenixbb] Twin refinement issues?

Anastassis Perrakis a.perrakis at nki.nl
Fri Apr 10 07:38:39 PDT 2009

Hi -

> I'm familiar with point group 32 and actually ran the program with  
> both
> indexings, which unexpectedly came up with roughly the same R-free
> (irony: the incorrect indexing was marginally better).  Mea culpa for
> not using my standard m.o. of comparing datasets using CCP4's SCALEIT.

Maybe the wrong place to preach the POINTLESS gospel, but its very nice
for comparing datasets (unmerged if you prefer) and forcing consistent  
indexing in CCP4.

> Auto-reindexing might be a time-saving feature (especially in point
> group 3) but should be consistent w/ and w/o twinning enabled and  
> needs
> to be much more prominently advertised in the output, and a new MTZ  
> file
> written.

Isn't it also a "philosophical" issue? How far should refinement  
programs go with this?
I would rather have a 52% twin fraction, so I go and re-index myself  
after seeing this
(if you like ccp4 reindex is good for it, and I strongly suspect there  
a single line command to do it using cctbx)
rather than this being done automagically and me ending up submitting  
the wrong combination of files to the
PDB (final model and 'scaled' data from before reindexing ...).

Anyway - I am happy that at least one person had the 52% twin - we had  
it a few years ago and it was fun to realize what was going on
(in P21)


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