You can always re-index a monoclinic unit cell with beta greater than 120deg.
Usually the beta closer to 90deg is preferred, but either will work. Bernie Santarsiero On May 21, 2014, at 11:54 AM, Roberto Battistutta wrote: > Dear All, > a question about C2 and I2 space groups. > Processing a dataset, XDS output says C2, with dimensions 122.8, 56,9 81,5 > and beta 125.1°. > Aimless reindexes to I2 with 81.6, 56.9, 101.1 and 96.2°. > Phenix (refine) returns a warning "NOTE: non-standard setting used: I 1 2 1". > In the PDB there are indeed several examples of I2 choices. > > The two space groups are equivalent as indicated in the International Tables > (all with number 5), but why different programs use different conventions? Is > there any rationale? By the way, the volumes of the two unit cells are very > similar. > > Thanks, > Roberto.
