Dear Gaoyina, I agree with Thassos that it is unlikely that your cell axes are all 90 Å long and more likely that you mentioned the angles. I also agree with Thassos that it would be best to run Pointless or Xtriage.
However, I think it is also good to try to determine the space group yourself, since that way one learns and understands how crystals are packed. Here are some comments from my side: For P4, as Thassos mentioned, the length of a should be equal to b since they are related by the 4-fold axis. Your self rotation functions show a strong peak for Chi=90, which suggest a 4-fold axis. However, there are also strong peaks in the Chi=180 sections, which suggest that you may have 2-folds as well, pointing to 422 symmetry. You can test this hypothesis by calculating the Matthews number (in ccp4i: Cell content analysis under molecular replacement) to see if at least 8 molecules would fit into the unit cell. For this calculation, you can ignore the possible presence of screw axis. Since you were running Molrep, I suppose you are going to solve the structure by molecular replacement. In this case you can also try brute force all possible space groups: P4x, P2x2x2x, P4x2x2. Make sure that all possible combinations of screw axes are tested. Normally, molecular replacement programs will do this automatically. Finally, the space group estimate of Pointless or Xtriage cannot be better than your data, especially when determining whether a reflection is extinct or not, so the true space group may be different from what Pointless ore Xtriage may suggest. Here your molecular replacement results have the final word. Good luck! Herman -----Ursprüngliche Nachricht----- Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von ??? Gesendet: Mittwoch, 15. April 2015 07:56 An: CCP4BB@JISCMAIL.AC.UK Betreff: [ccp4bb] problem in space group!! Dear all, Recentely I have got a dataset of 3.0A resolution and I have a big problem in choosing space group because the crystal were found in both P4,P1and P222 space groups,here are the figures of self rotation function on P4,P1 and P222 performed by MOLREP program for your reference. The unit cell parameters of P1 space group is a=90,b=90,c=90 Many thanks for any advices..!!! Best wishes, ynK
