I am refining a twinned dataset in possible spacegroup P212121 . Pointless thinks it is P43212 , but based on reading this posting ( http://www.phenix-online.org/pipermail/phenixbb/2007-September/000501.html) I think it is P212121.
The starting R/Rfree after molecular replacement ( single site mutant) was 34/38 to 2.2 A After an initial round of restrained refinement ( without twin refinement) and minimal rebuilding I got the R/Rfree to 30/34 Then I did an amplitude based twin refinement - The twin fraction was 0.48 k,h,-l and 0.52 h,k,l and The r/rfree became 24/29 After a little more rebuilding ( a few residues out of 800 residues in ASU) and another twin refinement I got an r/rfree of 22/27 . Now the twin fraction was 0.87 (h,k,l) and 0.13 (k,h,-1) The maps looked a little better allowing me to fix a few more residues Finally the same twin refinement gives me no twin operators and the R/Rfree is 22/26 All the twinning tests indicate a serious twinning in my crystal. Any ideas why I am seeing this Hari
