Hi Randy,
> As Jacob and others have mentioned, you will always get lower R-factors once > you treat the data as being twinned, and the more twin operators the bigger > the reduction in R-factors. Do normal data with no twinning, but refined with twin operator(s), show similar phenomenon? If it decreases R-factors for normal data, how much it can achieve (5-10% lower)? Thanks, Lan > So you need very strong evidence, independent of R-factors, to invoke > twinning. In this case, the L-test should be reasonably trustworthy even in > the presence of tNCS, and your L-test values are close to what one would > expect for an untwinned crystal. At most you have partial twinning, or > perhaps twinning of a pseudo-symmetric crystal (a possibility Phil > mentioned), where the effects on intensity statistics are reduced. > > One way to address a problem like this is to solve the structure in a lower > symmetry space group (as you have done), but then to check whether the MR > solution actually obeys the higher symmetry. You can do this by looking at > the crystal packing or at merging statistics for Fcalcs after a refinement > with highly restrained NCS. A similar sort of analysis is automated in the > Zanuda tool in CCP4. > > Dealing with potential complications from combinations of twinning and > pseudosymmetry is one of the more challenging aspects of crystallography, but > it's a good learning experience. Good luck! > > Randy Read > >> On 10 Jan 2019, at 22:38, Donghyuk Shin <sdh...@gmail.com> wrote: >> >> Dear all, >> >> Thank you very much for all of your suggestions and sharing experiences. >> As many of you commented, the current small unit cell C2 refinement seems to >> be incorrect or correct, and I should put some efforts to crack this >> question. >> >> - To Phill Jeffrey, >> The idea, trying to find high symmetry SG with small unit cell C2 data is >> good idea, and I will try this. >> For your last comments, identifiable electron density differences between >> each chain, >> I guess there should not be other densities between chains if my current SG >> and model is correct. Am I right? >> >> - To Ethan, >> Turning off the automatic_tNCS_option seems to be good option. >> I think, my current data seems to be twinned then tNCS which I am not sure >> at this moment. But I will keep your advice in my mind. >> >> - To Phoebe A. Rice, >> It is quite interesting that you also could get structure solution by >> indexing strong spots and having smaller unit cell. >> Actually, I was wondering how it was possible that having half-sized unit >> cell could have solution, while full-sized unit cell could not. >> It will be great if you can share your experience a bit more (e.g the size >> of smaller unit cell used in initial search for both 1szp and 3pkz) >> >> Again, thank you very much for all of your suggestion. >> >> Best wishes, >> Donghyuk >> >> ######################################################################## >> >> To unsubscribe from the CCP4BB list, click the following link: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.jiscmail.ac.uk_cgi-2Dbin_webadmin-3FSUBED1-3DCCP4BB-26A-3D1&d=DwIFAg&c=dIAUvHjI5lMnDD45iB3vgA&r=SZfWxbou0cinb5MH936uQKMweCFFe1qb2Aj8yA2JJ_E&m=1tRkoB-BHhBWDCtbPikRHJfYIDIqpaGbVoF5xFjTLD4&s=007v9D7bqs0h2uVFwau-m4cmT4PVlWyYZ2UVxJvWkrs&e= > > ------ > Randy J. Read > Department of Haematology, University of Cambridge > Cambridge Institute for Medical Research Tel: + 44 1223 336500 > Wellcome Trust/MRC Building Fax: + 44 1223 336827 > Hills Road E-mail: rj...@cam.ac.uk > Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk > > ######################################################################## > > To unsubscribe from the CCP4BB list, click the following link: > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.jiscmail.ac.uk_cgi-2Dbin_webadmin-3FSUBED1-3DCCP4BB-26A-3D1&d=DwIFAg&c=dIAUvHjI5lMnDD45iB3vgA&r=SZfWxbou0cinb5MH936uQKMweCFFe1qb2Aj8yA2JJ_E&m=1tRkoB-BHhBWDCtbPikRHJfYIDIqpaGbVoF5xFjTLD4&s=007v9D7bqs0h2uVFwau-m4cmT4PVlWyYZ2UVxJvWkrs&e= ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
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