data_Ba3Si
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.05
_cell_length_b   6.05
_cell_length_c   6.05
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Ba3Si
_chemical_formula_sum   'Ba3 Si1'
_cell_volume   156.46
_cell_formula_units_Z   1
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
  Ba  Ba0  1  0.14  0.14  0.14  1.0
  Ba  Ba1  1  0.28  0.28  0.28  1.0
  Ba  Ba2  1  0.42  0.42  0.42  1.0
  Si  Si3  1  0.0  0.0  0.0  1.0

data_Ba3Si
_symmetry_space_group_name_H-M   R3m
_cell_length_a   6.05
_cell_length_b   6.05
_cell_length_c   14.82
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Ba3Si
_chemical_formula_sum   'Ba9 Si3'
_cell_volume   469.37
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+1/3, y+2/3, z+2/3'
  8  '-y+1/3, x-y+2/3, z+2/3'
  9  '-x+y+1/3, -x+2/3, z+2/3'
  10  '-y+1/3, -x+2/3, z+2/3'
  11  '-x+y+1/3, y+2/3, z+2/3'
  12  'x+1/3, x-y+2/3, z+2/3'
  13  'x+2/3, y+1/3, z+1/3'
  14  '-y+2/3, x-y+1/3, z+1/3'
  15  '-x+y+2/3, -x+1/3, z+1/3'
  16  '-y+2/3, -x+1/3, z+1/3'
  17  '-x+y+2/3, y+1/3, z+1/3'
  18  'x+2/3, x-y+1/3, z+1/3'
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
  Ba  Ba0  3  0.0  0.0  0.58  1.0
  Ba  Ba1  3  0.0  0.0  0.72  1.0
  Ba  Ba2  3  0.0  0.0  0.86  1.0
  Si  Si3  3  0.0  0.0  0.0  1.0

Ba Ba Ba Si
Ba3Si crystallizes in the trigonal R3m space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted single-bond geometry to one Ba(2) and one Si(1) atom. The Ba(1)-Ba(2) bond length is 2.05 Å. The Ba(1)-Si(1) bond length is 2.05 Å. In the second Ba site, Ba(2) is bonded to one Ba(1), one Ba(3), and three equivalent Si(1) atoms to form distorted corner-sharing BaBa2Si3 trigonal bipyramids. The Ba(2)-Ba(3) bond length is 2.05 Å. All Ba(2)-Si(1) bond lengths are 3.59 Å. In the third Ba site, Ba(3) is bonded in a distorted single-bond geometry to one Ba(2) atom. Si(1) is bonded in a single-bond geometry to one Ba(1) and three equivalent Ba(2) atoms.