Hi Everybody, I am working in a P4212 plane group, which is a p4 symmetric structure with a screw axis in addition. My map has in the unit cell two 4-fold symmetric structures, one if which is upside-down with respect to the other one. If using expand in sftools, then the resulting map is p4 symmetrized in the center between two p4-symmetric structures, which is wrong. This is probably the phase origin problem referred to here: http://www.ccp4.ac.uk/dist/html/sftools.html#expand
Would anybody have a suggestion how I can expand the p4212 MTZ file to full p1, but with properly respecting the symmetry phase origin? My illiterate guess would be to either 1) shift the phase origin in the p4212 MTZ file by (180.0;0.0); then use sftools with "expand 1" to create the full reflection sets in p1; then shift back by (180.0;0.0); or 2) use sftools with the command "expand 1", and then modify (invert?) the phases of the reflections in the quadrants that have wrong phases. In option 1) I am not sure if it is possible to shift phase origin, while staying in p4212 symmetry. How could I do that? In option 2) I would probably get into deep water the next time I work with another symmetry, like p6212, or p2121, where I would have to deal not with quadrants but with triangles of 60deg angle? Any suggestions would be highly appreciated. All the best, Henning. Henning Stahlberg, PhD Prof. for Structural Biology, C-CINA, Biozentrum, University Basel Mattenstrasse 26 | D-BSSE | WRO-1058 | CH-4058 Basel | Switzerland http://c-cina.org | Tel. +41-61-387 32 62
