Dear CCTBX-list I am trying to reproduce the (scaled) intensities for Si reported here: http://rruff.geo.arizona.edu/AMS/xtal_data/DIFfiles/15285.txt based on this information: http://rruff.geo.arizona.edu/AMS/CIF_text_files/15285_cif.txt I am using CCTBX in Python: from cctbx.array_family import flex from cctbx import sgtbx, crystal, miller, xray sgnum = 227 sg = sgtbx.space_group_info(sgnum).group() latticepar = [5.43070, 5.43070, 5.43070, 90, 90, 90] dmin = 1.0 atompos = [['Si',(0.0, 0.0, 0.0)]] scatterers = flex.xray_scatterer() scatterers.append(xray.scatterer(label=atompos[0][0], site=atompos[0][1])) pg = sg.build_derived_point_group() sym = crystal.symmetry(space_group=sg,unit_cell=latticepar) sps = crystal.special_position_settings(crystal_symmetry=sym) structure = xray.structure(special_position_settings=sps,scatterers=scatterers) F = structure.structure_factors(d_min=dmin,algorithm='direct').f_calc() list(F.amplitudes()) This gives: [((0, 2, 2), 0.0), ((0, 4, 0), 120.21765812638594), ((1, 1, 1), 84.18849550806966), ((1, 3, 1), 65.48371727205928), ((1, 3, 3), 57.45438308324155), ((1, 5, 1), 51.48759686950681), ((2, 2, 2), 128.54540698861973), ((2, 4, 2), 0.0), ((3, 3, 3), 51.48759686950681)] How come CCTBX give an amplitude of 0.0 for (0,2,2) and (2,4,2)? The measured intensities in the DIFfile above does not show this. Am I missing something? Cheers, /Allan