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Acta Cryst. (1991). A47, 655-685

Looped and non-looped data items

The STAR File format permits any data item to be included in a loop_ list. This is also the case in a CIF. However, only data items which need to be repeated should appear in a looped list. Looped lists are composed of data items with common properties. For example, atom site information (represented by _atom_site_ items) may appear in one list and reflection data (represented by _refln_ items) in another, but they cannot be mixed together. Appendix II should be consulted for examples of looped lists.

Note that it is essential to loop repeated data items, rather than declaring them as a series of single data items. This is because the STAR format prohibits a data name from appearing more than once in a data block. The Dictionary identifies which individual data items will normally appear in looped lists. In most cases this is obvious from the nature of the data and its definition. Those data categories where individual items often appear in looped lists are summarized below:


_atom_site_
atomic site parameters
_atom_site_aniso_
atomic site anisotropic U values
_atom_type_
atom species
_cell_measurement_refln_
reflection data used in the unit-cell measurement
_chemical_conn_
chemical properties in connectivity table
_diffrn_attenuator_
diffraction attenuator scales
_diffrn_orient_refln_
reflections that define the diffractometer orientation matrix
_diffrn_radiation_wavelength_
discrete wavelengths used in diffraction measurements
_diffrn_refln_
diffraction intensity data
_diffrn_scale_group_
scale factors for groups of diffraction intensities
_diffrn_standard_refln_
standard reflections for scaling diffraction intensities
_exptl_crystal_
separate loops for crystals and crystal faces
_geom_angle_
interatomic angles
_geom_bond_
bond distances
_geom_contact_
contact distances
_geom_torsion_
torsion angles
_publ_author_address
authors' addresses
_publ_author_name
authors' names
_refln_
structure-factor reflection data
_reflns_scale_
scale factors for groups of structure-factor data
_symmetry_equiv_pos_as_xyz
space-group equivalent positions

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