I'd say its very likely to be orthorhombic. Refinement should tell you.....its the best way to determine the space group anyway. Why do you doubt its orthorhombic? Is Vm reasonable? It could be monoclinic and merohedrally winned with the beta angle very close to 90 degrees, but my money is on orthorhombic. if refinement fails I would try monoclinic plus/minus twinning. As for the operators, xxxxxx.triage will tell you and xxxxxx.refine will apply them for you during refinement....;-)
Bert ________________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] On Behalf Of Raji Edayathumangalam [r...@brandeis.edu] Sent: Friday, July 08, 2011 3:24 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Potential Space Group Issue Oops sorry for the slippery fingers. I meant h00, 0k0 and 00l in my original email and NOT "00h, 00k, 00l". Note the correction especially if you are a first-year graduate student trying to learn stuff from these emails :) Raji On Thu, Jul 7, 2011 at 11:30 PM, Raji Edayathumangalam <r...@brandeis.edu<mailto:r...@brandeis.edu>> wrote: Hello Everyone, I have a 3.1 Ang dataset for which I'd like to get to the bottom of what the correct space group is. The current unit cell in p212121 is 98.123 101.095 211.201 90.000 90.000 90.000 I fed the reflection data into Xtriage to look for twinning and pseudotranslational NCS and there is no indication for either issue in the Xtriage output. Also, all odd 00h, 00k, 00l reflections are systematically absent as they should be for p212121. However, my colleague who is also working on the same dataset recently reprocessed the data in P21. Here's the cell in p21: 98.010 100.940 210.470 90.00 90.04 90.00 p21 I am not sure if BETA=90.04 is significant enough to treat as p21 (0.04% deviation of beta angle from ideal lattice for p212121). I don't think so but I could be wrong. Could someone please clarify? Also, what kind of twinning and twinning operators can relate a p212121 cell to a p21 cell with almost identical unit cell parameters as that of the p212121 cell and leave all systematic absences intact? Thanks much. Raji ----------- Raji Edayathumangalam Instructor in Neurology, Harvard Medical School Research Associate, Brigham and Women's Hospital Visiting Research Scholar, Brandeis University -- ---------------------- Raji Edayathumangalam Instructor in Neurology, Harvard Medical School Research Associate, Brigham and Women's Hospital Visiting Research Scholar, Brandeis University
