[phenixbb] Re: twinning and translational NCS issues

Hi, Of the things Kay mentions that can go wrong, space group selection would be at the top of my list. Both twinning and translational NCS can confuse space group identification, and you can get things that appear to be solutions but are only partially correct so they don’t refine well. Nonetheless, you want to keep the rest of the possibilities in mind as well. Best wishes, Randy Read

On 16 Apr 2025, at 07:45, Kay Diederichs wrote:

Hi Wenhui Xi,

even with twinning and translational NCS, one does not expect Rfree to be nearly 60%. Rather such a high value points to the model being at least partially wrong or incomplete.

Even if you have a decent model for molecular replacement, the success of structure solution depends on the quality of the data. There are several things that can go wrong in data processing, in particular in indexing, spacegroup selection, shadow masking, radiation damage appraisal and selection of useful frame range and resolution. Wrong choices may prevent or at least impede structure solution.

I am one of the authors of the XDS program, and if you want I can look at your raw data with XDS (confidentially of course) and help you with processing. In that case, contact me off-list and send me a link to your raw data.

Best wishes, Kay _______________________________________________ phenixbb mailing list -- [email protected] To unsubscribe send an email to [email protected] Unsubscribe: phenixbb-leave@%(host_name)s

----- Randy J. Read Department of Haematology, University of Cambridge Cambridge Institute for Medical Research Tel: +44 1223 336500 The Keith Peters Building Hills Road E-mail: [email protected] Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk