Dear Donghyuk, Unfortunately, everything is possible when NCS, twinning etc. get into the game. I do not have answers, but some questions for you to think about: - Do you really have 6 twinning operators, or only one operator and are the other operators generated by (non)crystallographic symmetry? - Both your P6322 cell and your C2 cell have angles of 90 90 90. For P6322, the last angle should be 120 and for C2, only the second angle is constrained to be 90. Maybe you should check that not somewhere something went wrong with the cell angles. - How weak are the reflections that got discarded by halving the a- and b-axes? Do they have significant intensity, or is it only noise? - By shrinking the unit cell, you may have created artificial twinning when in the large unit cell the molecules are related by "twinning" (N)CS. - Since you seem to have found a solution with the small unit cell, you could see if you could fit this solution in the large unit cell: Process in P1 in the large unit cell and use the ensemble (the complete! unit cell of your C2 solution, as a search model. - Your current solution maybe correct after all, but I would analyze it very critically.
Best, Herman -----Ursprüngliche Nachricht----- Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Donghyuk Shin Gesendet: Donnerstag, 10. Januar 2019 11:12 An: CCP4BB@JISCMAIL.AC.UK Betreff: [EXTERNAL] [ccp4bb] translational NCS & twinning Dear all, I am having tough time with my Xtal data sets those seem to be twinned or have translational NCS, and it will be greatly appreciated if you can give me some advices or comments! Data was initially processed with XDS and scaled with aimless without specifying certain space group (SG). Aimless picked the P 63 2 2 for the best SG, but the xtriage indicates there is non-origin peak after patterson analysis. (attached log) And, I could not get the proper MR-solution from this data sets. Because I read that twinning and tNCS cannot be properly distinguished at high SG, I went down to subgroup either P32 or P6 assuming that there is twinning which make data set seems to have apparently high SG. (procedure was same XDS->aimless but I specified the SG to keep them) Then, xtriage still indicates there is non-origin peak as before, but found twin laws for the data sets (attached log). However, I still could not get the right MR-solution. Then, I went even further down to P3 or C2, and xtriage found more twin laws which is make sense because of the lower SG. (attached log) Again, I could not get the MR-solution. For all the MR running above, I assumed that phaser(ccp4 module) automatically applied tNCS if they present. or should I have to tick on button in the expert parameters? Then, I went back to the image and processed the datasets with mosflm by checking the indexed spots. During this step, I played with the threshold for indexing to follow the strong spot for get correct SG. I am not sure whether this is correct or not, but by putting high threshold for indexing (e.g. ~15) I could index the data with C2 which has half dimension for a,b axes (116.348, 67.218, 182.861, 90, 90, 90) to the original unit cell (232.533, 134.202, 182.67, 90, 90, 90). With this, I could put 3 molecules in ASU by MR. During refinement, I felt that the R values were not dropping, and I applied twin refinement. without twin refinement the R values were (0.39/0.44, work/free), and applying twin refinement gave me significantly better values (0.23/0.26). Because there were 6 twin operators which may cause this huge R value drop, I speculate whether this is true or not. Your comments will be greatly helpful! With you all the best, 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=DwIFaQ&c=Dbf9zoswcQ-CRvvI7VX5j3HvibIuT3ZiarcKl5qtMPo&r=HK-CY_tL8CLLA93vdywyu3qI70R4H8oHzZyRHMQu1AQ&m=xlZKtKm2eNS0qmQb4wXnIIknGL1-n0M0toJoWb2Ezco&s=scEheHieLBLhJMaXoEDimlYM9TAk600XwBjYXrQC1nc&e= ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1