_space_group.name_H-M_alt allows any Hermann-Mauguin symbol
to be given. The way in which this item is used is determined
by the user and in general is not intended to be interpreted by
computer. It may, for example, be used to give one of the
extended Hermann-Mauguin symbols given in Table 220.127.116.11 of
International Tables for Crystallography Vol. A (2002) or
a Hermann-Mauguin symbol for a conventional or unconventional
Each component of the space-group name is separated by a
space or an underscore. The use of a space is strongly
recommended. The underscore is only retained because it
was used in old CIFs. It should not be
used in new CIFs. Subscripts should appear without special
symbols. Bars should be given as negative signs before the
numbers to which they apply.
The commonly used Hermann-Mauguin symbol determines the space-
group type uniquely but a given space-group type may be
described by more than one Hermann-Mauguin symbol. The space-
group type is best described using _space_group.IT_number.
The Hermann-Mauguin symbol may contain information on the
choice of basis, but not on the choice of origin. To
define the setting uniquely, use _space_group.name_Hall or
list the symmetry operations.