data_CaFeSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.92
_cell_length_b   4.92
_cell_length_c   4.92
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaFeSe2
_chemical_formula_sum   'Ca1 Fe1 Se2'
_cell_volume   84.14
_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
  Fe  Fe1  1  0.22  0.22  0.22  1.0
  Se  Se2  1  0.48  0.48  0.48  1.0
  Se  Se3  1  0.74  0.74  0.74  1.0

data_CaFeSe2
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.92
_cell_length_b   4.92
_cell_length_c   12.05
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CaFeSe2
_chemical_formula_sum   'Ca3 Fe3 Se6'
_cell_volume   252.43
_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
  Fe  Fe1  3  0.0  0.0  0.78  1.0
  Se  Se2  3  0.0  0.0  0.26  1.0
  Se  Se3  3  0.0  0.0  0.52  1.0

Ca Fe Se Se
Ca Fe Se Se 0 1 o - o 0 1 - o o 0 1 o o - 0 1 o o o 0 3 - - - 0 3 - - o 0 3 - o - 0 3 o - - 0 2 - o o 0 2 o - o 0 2 o o - 1 3 - - o 1 3 - o - 1 3 o - - 1 2 - o o 1 2 o - o 1 2 o o - 1 2 o o o 2 3 - o o 2 3 o - o 2 3 o o - 2 3 o o o 
CaFeSe2 crystallizes in the trigonal R3m space group. Ca(1) is bonded in a 11-coordinate geometry to four equivalent Fe(1), three equivalent Se(1), and four equivalent Se(2) atoms. There is one shorter (2.61 Å) and three longer (3.17 Å) Ca(1)-Fe(1) bond lengths. All Ca(1)-Se(1) bond lengths are 3.33 Å. There are three shorter (2.97 Å) and one longer (3.14 Å) Ca(1)-Se(2) bond length. Fe(1) is bonded in a 8-coordinate geometry to four equivalent Ca(1) and four equivalent Se(1) atoms. There are three shorter (2.97 Å) and one longer (3.14 Å) Fe(1)-Se(1) bond length. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to three equivalent Ca(1) and four equivalent Fe(1) atoms. In the second Se site, Se(2) is bonded to four equivalent Ca(1) atoms to form distorted corner-sharing SeCa4 tetrahedra.