[phenixbb] generate Rfree flag for twinned crystals with 3 twin fractions

Peter Zwart PHZwart at lbl.gov
Sun Sep 19 08:37:18 PDT 2010

Free sets are always generated correctly within phenix.refine, it
looks like you have done the right thing.


On 19 September 2010 02:54, Zheng Zhou <zhengzhouzz at gmail.com> wrote:
> Dear all
> After reading the informative posts in mailing list, I started to deal
> with my first twinning dataset. The space group is P3. Xtriage found 3
> twin laws. R vs R statistics indicated perfect twinning for two twin
> laws and one is twin with RPS. I realize that twin-related reflections
> should be in the same work or free group. Could phenix handle the
> Rfree flag correctly for me when there are more than one twin fraction
> identified?
> By applying one twin law, the Rfree dropped from 37% to 28% using
> phenix. When I use Refmac, the twin fractions are refined and the
> Rfree is down to 26%. I copied the Rfree flag from phenix to the ccp4
> in this case. When I let ccp4 generate Rfree flag automatically, the
> Rfree is refined to 26% too. Should I label the Rfree at a higher
> space group?
> Thanks for your advice
> Best,
> Zheng (Joe) Zhou
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P.H. Zwart
Research Scientist
Berkeley Center for Structural Biology
Lawrence Berkeley National Laboratories
1 Cyclotron Road, Berkeley, CA-94703, USA
Cell: 510 289 9246
BCSB:      http://bcsb.als.lbl.gov
PHENIX:   http://www.phenix-online.org
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