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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