GULP-formatted CIF

When outputting a CIF from GULP, the formatting doesn’t seem to be perfect in terms of the expected spec for a CIF. Some of the CIF parsing programs I use (e.g. ASE) only work correctly if I modify the CIF slightly. Namely, there are two loop_ lines. My understanding is that loop_ should only be used for tables, so things like x,y,z coordinates, but I certainly could be wrong. There’s some additional discussion here.


_audit_creation_method             'generated by GULP'

_symmetry_space_group_name_H-M     '(unknown)       '
_symmetry_Int_Tables_number        1

_cell_length_a                        5.1053
_cell_length_b                        5.1053
_cell_length_c                        5.1053
_cell_angle_alpha                   60.0000
_cell_angle_beta                    60.0000
_cell_angle_gamma                   60.0000

  Cu          0.00000      0.00000      0.00000  1.0000
  Cu          0.00000      0.00000      0.50000  1.0000
  Cu          0.00000      0.50000      0.00000  1.0000
  Cu          1.00000      0.50000      0.50000  1.0000
  Cu          0.50000      0.00000      0.00000  1.0000
  Cu          0.50000      1.00000      0.50000  1.0000
  Cu          0.50000      0.50000      0.00000  1.0000
  Cu          0.50000      0.50000      0.50000  1.0000

I can’t claim to be an expert on the CIF file format either. I think this was modelled on the format found in a few other CIF files that I’d seen where the loop_ appeared multiple times to denote different sections of the information. It can easily be corrected if we get an expert opinion…