As far as I as I remember, sgroup finds and gives the standard space group corresponding to the structure:
In monoclinic systems there are two alternative standards in the International Tables: unique axis along b o unique axis along c. For instance, the Bilbao server normally uses the first one, but in some of its programs like WYCKPOS, it offers you the two possible standards. It seems that sgroup uses the second possible standard "unique axis c", and in your case it is only proposing a change to this standard setting. I do not think there is any error in the output of sgroup and in principle nothing should be changed, because when announcing the space group: "(C2/m) unique axis c", the "(C2/m)" here is only used as synonym of space group Number 12, and it does not mean that the centering translation is a "C" centering, i.e. (1/2 1/2 0), which is impossible if the c-axis is chosen as the monoclinic one. You can compare with the space group labels and positions in the lists offered by WYCKPOS in the Bilbao server. You will see that for the standard " (C2/m): unique axis c" , the centering translation is in fact of type "A", i.e. (0 1/2 1/2). Therefore, if you inspect the transformed structure proposed by sgroup, I would expect that you will find that it is just proposing to interchange the axes a and b, so that your B2/m (unique axis c) symmetry becomes in fact A2/m(unique axis c), which is the second standard and it is denoted by "(C2/m) unique axis c" (surely a very misleading notation, but it is not the fault of sgroup!). Regards, J. Manuel Perez-Mato Fac. Ciencia y Tecnologia, Universidad del Pais Vasco, UPV 48080 BILBAO, Spain tel. +34 946012473 fax. +34 946013500 ************************************************* On Wed, October 17, 2012 10:48 am, Peter Blaha wrote: > I'm not an expert in sgroup, but yes, I believe the printed "names" of all > monoclinic spacegroups which have > different names for the unique axis c (vs. b) are not correct and I'll change them to B or b (instead of C or c) > > As far as I know, it does not affect anything else then the "comment" in the struct-files generated by sgroup. > > > > Am 16.10.2012 14:04, schrieb Gavin Abo: >> Dear Prof. Blaha and developers, >> I believe the attached struct file has appropriate parameters for the "12_B2/m" spacegroup. After I run "x sgroup" in w2web in Wien2k 12.1, it >> says "sgroup found: 12 (C 2/m) >> [unique axis c] cell choice 2". I suppose that its most likely correct, >> but was just curious if perhaps the "C 2/m" is a typo and should be "B 2/m" in the character array >> "comnt_B_C2h_sgrp" in SRC_sgroup/sgrp_mon.c. >> Kind Regards, >> Gavin >> _______________________________________________ >> Wien mailing list >> Wien at zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > -- > > P.Blaha > -------------------------------------------------------------------------- Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna Phone: +43-1-58801-165300 FAX: +43-1-58801-165982 > Email: blaha at theochem.tuwien.ac.at WWW: > http://info.tuwien.ac.at/theochem/ > -------------------------------------------------------------------------- _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > >