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:

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_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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