data_[Mg6Se8]
loop_
 _atom_type_symbol
 _atom_type_electronegativity
 _atom_type_radius
 _atom_type_ionic_radius
[
  Mg  1.3100  1.5000  0.8600
  Se  2.5500  1.1500  1.0133
]
_symmetry_space_group_name_H-M [I4/mmm]
_cell_length_a [3.7466]
_cell_length_b [3.7466]
_cell_length_c [26.0955]
_cell_angle_alpha [90.0000]
_cell_angle_beta [90.0000]
_cell_angle_gamma [90.0000]
_symmetry_Int_Tables_number [139]
_chemical_formula_structural [Mg3Se4]
_chemical_formula_sum '[Mg6 Se8]'
_cell_volume [366.2957]
_cell_formula_units_Z [2]
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
[
  Mg  Mg0  4  0.0000  0.0000  0.2929  1
  Mg  Mg1  2  0.0000  0.0000  0.0000  1
  Se  Se2  4  0.0000  0.0000  0.1897  1
  Se  Se3  4  0.0000  0.0000  0.4527  1
]