data_KAsSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.13
_cell_length_b   5.13
_cell_length_c   5.13
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   KAsSe2
_chemical_formula_sum   'K1 As1 Se2'
_cell_volume   95.21
_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
  K  K1  1  0.0  0.0  0.0  1.0
  As  As0  1  0.62  0.62  0.62  1.0
  Se  Se2  1  0.81  0.81  0.81  1.0
  Se  Se3  1  0.44  0.44  0.44  1.0

data_KAsSe2
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.13
_cell_length_b   5.13
_cell_length_c   12.55
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   KAsSe2
_chemical_formula_sum   'K3 As3 Se6'
_cell_volume   285.62
_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
  K  K0  3  0.0  0.0  0.0  1.0
  As  As1  3  0.0  0.0  0.38  1.0
  Se  Se2  3  0.0  0.0  0.19  1.0
  Se  Se3  3  0.0  0.0  0.56  1.0

K As Se Se
K As Se Se 0 2 - - - 0 1 - - o 0 1 - o - 0 1 o - - 0 3 - o o 0 3 o - o 0 3 o o - 1 3 o o o 1 2 o o o 2 3 + o o 2 3 o + o 2 3 o o + 
KAsSe2 crystallizes in the trigonal R3m space group. K(1) is bonded in a distorted single-bond geometry to three equivalent As(1), one Se(1), and three equivalent Se(2) atoms. All K(1)-As(1) bond lengths are 3.01 Å. The K(1)-Se(1) bond length is 2.36 Å. All K(1)-Se(2) bond lengths are 3.23 Å. As(1) is bonded to three equivalent K(1), one Se(1), and one Se(2) atom to form AsK3Se2 trigonal bipyramids that share corners with three equivalent Se(2)K3As tetrahedra, corners with six equivalent As(1)K3Se2 trigonal bipyramids, and edges with three equivalent Se(2)K3As tetrahedra. The As(1)-Se(1) bond length is 2.36 Å. The As(1)-Se(2) bond length is 2.36 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted linear geometry to one K(1) and one As(1) atom. In the second Se site, Se(2) is bonded to three equivalent K(1) and one As(1) atom to form distorted SeK3As tetrahedra that share corners with six equivalent Se(2)K3As tetrahedra, corners with three equivalent As(1)K3Se2 trigonal bipyramids, and edges with three equivalent As(1)K3Se2 trigonal bipyramids.