Hello, I have some trouble with cctbx, I try to understand why and I do not succeed. I need your help ! I replaced quartz with silicon in the "beach in the box" example/tutorial. This is the resulting code : from cctbx import xray from cctbx import crystal from cctbx.array_family import flex silicon_structure = xray.structure( special_position_settings=crystal.special_position_settings( crystal_symmetry=crystal.symmetry( unit_cell=(5.4307,5.4307,5.4307,90,90,90), space_group_symbol="Fd3m")), scatterers=flex.xray_scatterer([ xray.scatterer( label="Si", site=(0.,0.,0.), u=0) ])) silicon_structure.show_summary().show_scatterers() for scatterer in silicon_structure.scatterers(): print "%s:" % scatterer.label, "%8.4f %8.4f %8.4f" % scatterer.site site_symmetry = silicon_structure.site_symmetry(scatterer.site) print " point group type:", site_symmetry.point_group_type() print " special position operator:", site_symmetry.special_op() f_calc = silicon_structure.structure_factors(d_min=1).f_calc() f_calc.show_summary().show_array() and running the script gives the following result result : Number of scatterers: 1 At special positions: 1 Unit cell: (5.4307, 5.4307, 5.4307, 90, 90, 90) Space group: F d -3 m :2 (No. 227) Label, Scattering, Multiplicity, Coordinates, Occupancy, Uiso Si Si 16 ( 0.0000 0.0000 0.0000) 1.00 0.0000 Si: 0.0000 0.0000 0.0000 point group type: -3m special position operator: 0,0,0 Miller array info: None Observation type: None Type of data: complex_double, size=9 Type of sigmas: None Number of Miller indices: 9 Anomalous flag: False Unit cell: (5.4307, 5.4307, 5.4307, 90, 90, 90) Space group: F d -3 m :2 (No. 227) (0, 2, 2) 0j (0, 4, 0) (120.217658126+0j) (1, 1, 1) (-84.1884955081+0j) (1, 3, 1) (65.4837172721+0j) (1, 3, 3) (57.4543830832+0j) (1, 5, 1) (-51.4875968695+0j) (2, 2, 2) (128.545406989+0j) (2, 4, 2) 0j (3, 3, 3) (-51.4875968695+0j) The 220 structure factor, at least, does not look correct . I do not understand the 16 multiplicity either. Is there something I miss ? Best regards Marc