Dear All, I am trying to convert from a conventional cell to a primitive cell using cctbx, but I am having some problems. What I do is the following: 1) I construct a spaceGroup object using the space group symbol 2) I retrieve the change of basis operator using z2p_op() from the space group object 3) I apply this operator to the conventional cell 4) I take a list of symmetry unique atoms and apply the operator to their fractional coordinates At this point I have a primitive cell which agrees exactly with what I get from other codes. The problem comes when I am trying to construct all atoms from the symmetry unique ones. I do this by the following procedure: 5) I take the space group object and call its change_basis() method with the z2p_op() operator 6) I loop over all order_z() symmetry operations in the space group applying the operation to the fractional coordinates making sure that I don't create two atoms at the same position The whole procedure works well, e. g., for cubic crystals. However, if I take a hexagonal crystal (e. g., Cr2O3, R -3 c) the crystal build by steps 5 and 6 above is not correct. In this case the conventional cell has a=b != c, alpha=beta=90, and gamma=120, but the primitive cell has a=b=c and alpha=beta=gamma. I have tried to add ":R" to the space group symbol and constructing a new spaceGroup object in step 5 above, but that does not make any difference. What do I have to do to build the crystal in this case or what is wrong with my procedure ? Best Regards, Jörg-Rüdiger Hill -- ------------------------------------------------------------------------------- Dr. Jörg-Rüdiger Hill Tel.: +33 1 53 43 51 05 Director R & D Tel. (direct): +49 89 613 05 700 Scienomics Fax: +33 1 53 43 92 92 17 Square Edouard VII E-Mail: [email protected] 75009 Paris, France Web: http://www.scienomics.com/ -------------------------------------------------------------------------------