_symmetry_Int_Tables_number
Space-group number from International Tables for Crystallography
Vol. A (2002).

_cell_length_a
_cell_length_b
_cell_length_c
_cell_angle_alpha
_cell_angle_beta
_cell_angle_gamma
Unit cell parameters. Cell lengths are in Ångström and angles are
in degree.

_atom_site_label
A unique identifier for a particular site in the crystal. Typically
this will be the chemical symbol of the atom occupying this site,
optionally followed by an number (e.g. "Cu1"), an underscore
(e.g. "Zn_Zn_301_A_O") or an asterix (e.g. H*251). Other labels are
possible, but not considered here.

_atom_site_type_symbol (optional)
A code to identify the atom species (singular or plural) occupying
this site. Typically the chemical symbol of the atom species
(e.g. "Ni").

_atom_site_site_symmetry_multiplicity (optional)
The number of different sites that are generated by the application of
the space-group symmetry to the coordinates given for this site. It is
equal to the multiplicity given for this Wyckoff site in International
Tables for Crystallography Vol. A (2002).

_atom_site_Wyckoff_symbol (optional)
The Wyckoff symbol (letter) as listed in the space-group tables of
International Tables for Crystallography Vol. A (2002).

_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
Atom-site coordinates as fractions of the _cell_length_ values.

_atom_site_occupancy (optional)
The fraction of the atom type present at this site. The sum of the
occupancies of all the atom types at this site may not exceed 1.0.