Hi, yes, that would be my preferred strategy: often (but not always), sampling space by trying plausible options saves you more time than thinking hard first... and then still ending up trying -:)
All the best, Pavel. On Fri, Jul 8, 2011 at 1:07 PM, Van Den Berg, Bert < lambertus.vandenb...@umassmed.edu> wrote: > 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 >
