A few comments -
you dont give your cell dimensions but if they are more or less the same
for the P212121 and P43 21 2 I dont see how a 43 set of absences can
turn into a 21 set ..
However if there is non-crystallographic translation, then absences an
mislead.. Is that true for you -
Twinning tests can also be very deceptive if there is
non-crystallographic translation, but I admit they usually hide it
rather than display false twinning...
Eleanor
hari jayaram wrote:
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
