data_CaSi2Se
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.89
_cell_length_b   4.89
_cell_length_c   4.89
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaSi2Se
_chemical_formula_sum   'Ca1 Si2 Se1'
_cell_volume   82.86
_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  0.46  0.46  0.46  1.0
  Si  Si2  1  0.0  0.0  0.0  1.0
  Si  Si3  1  0.19  0.19  0.19  1.0
  Se  Se1  1  0.73  0.73  0.73  1.0

data_CaSi2Se
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.89
_cell_length_b   4.89
_cell_length_c   11.99
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CaSi2Se
_chemical_formula_sum   'Ca3 Si6 Se3'
_cell_volume   248.58
_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  0.54  1.0
  Si  Si1  3  0.0  0.0  0.0  1.0
  Si  Si2  3  0.0  0.0  0.81  1.0
  Se  Se3  3  0.0  0.0  0.27  1.0

Ca Si Si Se
CaSi2Se crystallizes in the trigonal R3m space group. Ca(1) is bonded in a 11-coordinate geometry to three equivalent Si(1), four equivalent Si(2), and four equivalent Se(1) atoms. All Ca(1)-Si(1) bond lengths are 3.21 Å. There are three shorter (2.93 Å) and one longer (3.23 Å) Ca(1)-Si(2) bond length. There are three shorter (2.93 Å) and one longer (3.23 Å) Ca(1)-Se(1) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to three equivalent Ca(1), one Si(2), and three equivalent Se(1) atoms. The Si(1)-Si(2) bond length is 2.28 Å. All Si(1)-Se(1) bond lengths are 2.93 Å. In the second Si site, Si(2) is bonded to four equivalent Ca(1) and one Si(1) atom to form distorted SiCa4Si trigonal bipyramids that share corners with four equivalent Se(1)Ca4Si3 hexagonal pyramids, corners with twelve equivalent Si(2)Ca4Si trigonal bipyramids, edges with three equivalent Se(1)Ca4Si3 hexagonal pyramids, and faces with three equivalent Se(1)Ca4Si3 hexagonal pyramids. Se(1) is bonded to four equivalent Ca(1) and three equivalent Si(1) atoms to form distorted SeCa4Si3 hexagonal pyramids that share corners with six equivalent Se(1)Ca4Si3 hexagonal pyramids, corners with four equivalent Si(2)Ca4Si trigonal bipyramids, edges with six equivalent Se(1)Ca4Si3 hexagonal pyramids, edges with three equivalent Si(2)Ca4Si trigonal bipyramids, and faces with three equivalent Si(2)Ca4Si trigonal bipyramids.