Data type: char
Must appear in a looped list
May match values of '_atom_site_aniso_label' '_geom_angle_atom_site_label_1' '_geom_angle_atom_site_label_2' '_geom_angle_atom_site_label_3' '_geom_bond_atom_site_label_1' '_geom_bond_atom_site_label_2' '_geom_contact_atom_site_label_1' '_geom_contact_atom_site_label_2' '_geom_hbond_atom_site_label_D' '_geom_hbond_atom_site_label_H' '_geom_hbond_atom_site_label_A' '_geom_torsion_atom_site_label_1' '_geom_torsion_atom_site_label_2' '_geom_torsion_atom_site_label_3' '_geom_torsion_atom_site_label_4'
The _atom_site_label is a unique identifier for a particular site in the crystal. This code is made up of a sequence of up to seven components, _atom_site_label_component_0 to *_6, which may be specified as separate data items. Component 0 usually matches one of the specified _atom_type_symbol codes. This is not mandatory if an _atom_site_type_symbol item is included in the atom site list. The _atom_site_type_symbol always takes precedence over an _atom_site_label in the identification of the atom type. The label components 1 to 6 are optional, and normally only components 0 and 1 are used. Note that components 0 and 1 are concatenated, while all other components, if specified, are separated by an underline character. Underline separators are only used if higher-order components exist. If an intermediate component is not used it may be omitted provided the underline separators are inserted. For example the label 'C233__ggg' is acceptable and represents the components C, 233, '', and ggg. Each label may have a different number of components.