[phenixbb] Twin refinement issues?

[Phil Jeffrey]

While experimenting with twin refinement for a crystal in P321 that 
approximates P622 to varying extents, I noticed:

| twin fraction: 0.59  twin operator: -h,-k,l 
       |

A bug, perhaps ?

This twin fraction would seem to be unlikely, since twin fractions > 0.5 
have no meaning.  Since this data does not scale well in p622 compared 
to some more heavily-twinned datasets on this xtal form I think the twin 
fraction is certainly less than 0.5.

Xtriage estimates:
Statistics depending on twin laws
-----------------------------------------------------------------
| Operator | type | R obs. | Britton alpha | H alpha | ML alpha |
-----------------------------------------------------------------
| -h,-k,l  |   M  | 0.150  | 0.343         | 0.347   | 0.283    |
-----------------------------------------------------------------


Unless of course phenix.refine is reporting 2*alpha.

Phenix v1.4-3  Intel Mac OSX 10.5.6

This particular run with:

phenix.refine model-08.pdb pz7e_truncate-unique.mtz 
refinement.main.ncs=true strategy=individual_sites+group_adp --overwrite 
xray_data.r_free_flags.generate=True twin_law="-h,-k,l"

This is a very early non-finessed model.

Phil Jeffrey
Princeton