Hi Peter, > I have a P21 case with some strange ratios in the cell dimensions : > a, b=a, c=1.5a, 90, 105, 90. The native patterson shows a strong > peak (40% of origin) at (x,0.5,0) indicating some pseudo symmetry. > Such cell dimension and peak prompted me to think that the actual > space group is side-centered.
See below. (To give proper credit: explore_metric_symmetry was written by Peter Zwart.) Ralf % phenix.explore_metric_symmetry --unit-cell=1,1,1.5,90,105,90 --space-group=p21 A summary of the constructed point group graph object is given below ==================================================================== ---------------------- Input crystal symmetry ---------------------- Unit cell: (1.0, 1.0, 1.5, 90.0, 105.00000000000001, 90.0) Unit cell volume: 1.44888873943 Space group: P 1 21 1 -------------------------- Lattice symmetry deduction -------------------------- Niggli cell: (1.0, 1.0, 1.5, 90.0, 105.00000000000001, 90.0) Niggli cell volume: 1.44888873943 Niggli transformed input symmetry: P 1 21 1 Symmetry of Niggli cell: C 2 2 2 (x+y,z,2*x) All pointgroups that are both a subgroup of the lattice symmetry and a supergroup of the Niggli transformed input symmetry wil now be listed, as well as their minimal supergroups/maximal subgroups and symmetry operators that generate them. For each pointgroup, a list of compatible spacegroups will be listed. Care is taken that there are no sysmetatic absence violation with the provided input spacegroup. ------------------------ Vertices and their edges ------------------------ Point group P 1 2 1 is a maximal subgroup of : * C 2 2 2 (x+y,z,2*x) Point group C 2 2 2 (x+y,z,2*x) is a maximal subgroup of : * None ------------------------- Transforming point groups ------------------------- >From P 1 2 1 to C 2 2 2 (x+y,z,2*x) using : * h,-k,-h-l ---------------------- Compatible spacegroups ---------------------- Spacegroups compatible with a specified point group **and** with the systematic absenses specified by the input space group, are listed below. Spacegroup candidates in point group P 1 2 1: * P 1 21 1 1.00 1.00 1.50 90.00 105.00 90.00 Spacegroup candidates in point group C 2 2 2 (x+y,z,2*x): * C 2 2 21 1.00 2.91 1.00 90.00 90.00 90.00
