Contains all the data items that refer to the space group as a
whole, such as its name or crystal system. They may be looped,
for example, in a list of space groups and their properties.
Only a subset of the SPACE_GROUP category items appear in
this dictionary. The remainder are found in the symmetry CIF
Space-group types are identified by their number as given in
International Tables for Crystallography Vol. A. Specific
settings of the space groups can be identified either by their
Hall symbol or by specifying their symmetry operations.
The commonly used Hermann-Mauguin symbol determines the
space-group type uniquely but several different Hermann-Mauguin
symbols may refer to the same space-group type. A Hermann-Mauguin
symbol contains information on the choice of the basis, but not
on the choice of origin. Different formats for the
Hermann-Mauguin symbol are found in the symmetry CIF dictionary.