 |
 |
Clemens is right of course. If you ignore the lattice centring in C2, the cells are the same. I was however under the impression that auto-indexing goes via the primitive cell. Which makes the two solutions unique. Ignoring the possible lattice translation in P2 will show up in a Patterson function (at 1/2,1/2,0 i think) . The lattice translation might of course be a pseudo translation. In the C2 case, you would miss weak reflections if P2 would be the right answer. P 2008/5/1 Clemens Vonrhein <[log in to unmask]>: > Dear Junyu, > > it looks to me like you encounter a classical monoclinic feature: one > can index monoclinic always in two ways > > > origin > | > V > > A' ---------------------------------- A > \ /\ / > \ / \ / > \ / \ / > \ / \ / > \ / \ / > \ / \ / > \ / \ / > \ / \ / > /________________/ > > C C' > > One cell (A,B,C) has B coming towards you and the other (A',B',C') has > B' pointing away from you. The two axes A and A' have identical length > as have B and B'. But C' is the diagonal in the AC-plane. > > In your case you can just swap the A and C axis of the C2 (to follow > the above picture) and then calculate the C' (diagonal) to 136.8. > > So to summarize: these are identical cells - just different choice > of axes (and nothing to do with the C2 versus P2 choice ... I think). > > Cheers > > Clemens > > > > > On Thu, May 01, 2008 at 12:03:16PM -0400, Junyu Xiao wrote: > > Hi all, > > > > We run into an interesting space group problem. The same diffraction > > image can be either indexed into space group C2, with a=145, b=44, > > c=67, and beta=110.5; or space group P2 (should be P21 after > > scaling), with a=67, b=44, c=136, and beta=96.8. Both are refined ok > > during index. These two must somehow be related. Can anyone give some > > comments on that? > > > > Thanks a lot, > > Junyu > > > > ================================= > > Junyu Xiao > > Department of Biological Chemistry, > > University of Michigan > > > > Lab address: > > 3163 Life Sciences Institute, > > University of Michigan, > > 210 Washtenaw Avenue > > Ann Arbor, MI, 48109-2216 > > Phone: 734-615-2078 > > ================================== > > > > > > > > -- > > *************************************************************** > * Clemens Vonrhein, Ph.D. vonrhein AT GlobalPhasing DOT com > * > * Global Phasing Ltd. > * Sheraton House, Castle Park > * Cambridge CB3 0AX, UK > *-------------------------------------------------------------- > * BUSTER Development Group (http://www.globalphasing.com) > *************************************************************** > -- ----------------------------------------------------------------- P.H. Zwart Beamline Scientist Berkeley Center for Structural Biology Lawrence Berkeley National Laboratories 1 Cyclotron Road, Berkeley, CA-94703, USA Cell: 510 289 9246 BCSB: http://bcsb.als.lbl.gov PHENIX: http://www.phenix-online.org CCTBX: http://cctbx.sf.net -----------------------------------------------------------------