Hi Alex, You are not giving the number after refinement without the twin refinement. Nevertheless, R-free drops like this are not unheard of. You should check your Refmac log file, it would warn you of potential space group errors. Refmac will also give you a refined estimate of the twin fraction.
Cheers, Robbie Sent from my Windows 10 phone Van: Alex Lee<mailto:alexlee198...@gmail.com> Verzonden: donderdag 13 april 2017 19:19 Aan: CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK> Onderwerp: [ccp4bb] Refmac5 twin refinement pushing Rfree surprisingly down Dear All, I have a protein/dna complex crystal and data collected at 3A and another set at 2.8A, space group P32. L test shows twinning (fraction around 0.11). The structure solved by MR and model building of the complex finish (no solvent built yet, I do not think it's good to build solvent in such low resolution data). I did Refmac5 to refine my structure (restraint refinement) with or without twinning, to my surprise, the Rfree drops a lot after twin refinement of two data sets. Summary below: 2.8A dataset: before twin refine 34%, 29%; after twin refine:24%, 19% 3A dataset: before twin refine 30%;26%; after refine 25%, 18% I know that a lot of threads in CCP4bb talking about Rfree after twin refine and Rfree without twin refine can not compare directly. By drop R free this much by twin refine, it gives me a feeling of too good to be true (at such low resolution with such good Rfree, maybe overrefined a lot?), but from the density map after twin refine, it does seem better than no twin refine map. I do not know if reviewers are going to challenge this part. Any input is appreciated.
