I2 and C2 are different settings of the same group. The official IUCr convention is to use the one which gives the beta angle closer to 90 degrees. As far as I know all programs should now be able to use the I2 setting, but if it worries you, you can reindex to C2
Phil On 21 May 2014, at 17:54, Roberto Battistutta <[email protected]> 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. > > > Roberto Battistutta > Associate Professor > Department of Chemistry > University of Padua > via Marzolo 1, 35131 Padova - ITALY > tel. +39.049.827.5262 > fax. +39.049.827.5829 > [email protected] > www.chimica.unipd.it/roberto.battistutta/ > VIMM (Venetian Institute of Molecular Medicine) > via Orus 2, 35129 Padova - ITALY > tel. +39.049.7923.236 > fax +39.049.7923.250 > www.vimm.it
