Hello Garib, I was using the ouput from a refmac run for the next round and using what I thought were the original fobs . So I guess as you said at each round I was using the de-twinned result from the previous round.
I will repeat these refinements with the original scala output mtz to get a more accurate feel for the twin fraction. I am using medium restraints with NCS ( I have four molecules in the asu) and the data does also look like P43212 with fewer molecules in the ASU. Thank you for all your suggestions Hari On Fri, Apr 23, 2010 at 5:38 PM, Garib Murshudov <[email protected]>wrote: > You may be using output reflection data from the previous cycle of > refinement for the next session. After twin refinement output Fobs > (confusingly) may be detwinned. You can try to use original reflection data > file (e.g. after scala/truncate/freerflag) and for refinement and it may > clarify things a bit. If you are using original reflection data file for > refinement then I do not knwo the reason of such peculiar behaviour. > > I have seen that twin fraction during refinement goes down but I am not > sure that it would happen substatioally if your R/Rfree were as you stated > before twin refinement. > > regards > Garib > > On 23 Apr 2010, at 22:28, 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 > > > > >
