data_CaSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.11
_cell_length_b   5.11
_cell_length_c   5.11
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaSe3
_chemical_formula_sum   'Ca1 Se3'
_cell_volume   94.23
_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
  Ca  Ca0  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.81  0.81  0.81  1.0
  Se  Se2  1  0.61  0.61  0.61  1.0
  Se  Se3  1  0.42  0.42  0.42  1.0

data_CaSe3
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.11
_cell_length_b   5.11
_cell_length_c   12.51
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CaSe3
_chemical_formula_sum   'Ca3 Se9'
_cell_volume   282.68
_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
  Ca  Ca0  3  0.0  0.0  0.0  1.0
  Se  Se1  3  0.0  0.0  0.19  1.0
  Se  Se2  3  0.0  0.0  0.39  1.0
  Se  Se3  3  0.0  0.0  0.58  1.0

Ca Se Se Se
Ca Se Se Se 0 1 - - - 0 2 - - o 0 2 - o - 0 2 o - - 0 3 - o o 0 3 o - o 0 3 o o - 1 2 o o o 1 3 + o o 1 3 o + o 1 3 o o + 2 3 o o o 
CaSe3 crystallizes in the trigonal R3m space group. Ca(1) is bonded in a 1-coordinate geometry to one Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. The Ca(1)-Se(1) bond length is 2.43 Å. All Ca(1)-Se(2) bond lengths are 3.03 Å. All Ca(1)-Se(3) bond lengths are 3.13 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to one Ca(1) and one Se(2) atom. The Se(1)-Se(2) bond length is 2.43 Å. In the second Se site, Se(2) is bonded to three equivalent Ca(1), one Se(1), and one Se(3) atom to form distorted SeCa3Se2 trigonal bipyramids that share corners with three equivalent Se(3)Ca3Se tetrahedra, corners with six equivalent Se(2)Ca3Se2 trigonal bipyramids, and edges with three equivalent Se(3)Ca3Se tetrahedra. The Se(2)-Se(3) bond length is 2.43 Å. In the third Se site, Se(3) is bonded to three equivalent Ca(1) and one Se(2) atom to form distorted SeCa3Se tetrahedra that share corners with six equivalent Se(3)Ca3Se tetrahedra, corners with three equivalent Se(2)Ca3Se2 trigonal bipyramids, and edges with three equivalent Se(2)Ca3Se2 trigonal bipyramids.