Dear All, I'm trying to decide the spacegroup between P21 and C2 and in need of your help. I have a data with the following possible cells: P21: 41.8500 119.4800 93.2600 90.0000 102.8880 90.0000 C2: 181.8000 41.8400 119.5300 90.0000 90.0820 90.0000
The data is twinned (C2221 is always suggested by different programs without considering twinning). Therefore twin refinement is carried on in
Phenix.refine, with twin law "h,-k,-h-l" for P21 and "h,-k,-l" for C2. Both space groups give a reasonable but not so different R-free close to 23% for a 2.3 angstrom data, and the resulted map is also OK in both cases. As it is with higher symmetry, maybe I should go with C2. But there could be something I missed here, i.e. a pseudosymmetry operator taken as crystallographic symmetry? Any suggestions or comments are highly appreciated! Thanks, Hua
