data_Si2As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.66
_cell_length_b   5.66
_cell_length_c   6.71
_cell_angle_alpha   110.42
_cell_angle_beta   110.42
_cell_angle_gamma   39.41
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Si2As
_chemical_formula_sum   'Si4 As2'
_cell_volume   126.89
_cell_formula_units_Z   2
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
  Si  Si2  1  0.36  0.0  0.36  1.0
  Si  Si3  1  0.14  0.0  0.54  1.0
  Si  Si4  1  0.05  0.0  0.69  1.0
  Si  Si5  1  0.82  0.0  0.86  1.0
  As  As0  1  0.74  0.0  0.23  1.0
  As  As1  1  0.44  0.0  1.0  1.0

data_Si2As
_symmetry_space_group_name_H-M   P-1
_cell_length_a   3.82
_cell_length_b   5.66
_cell_length_c   6.71
_cell_angle_alpha   110.42
_cell_angle_beta   90.0
_cell_angle_gamma   109.71
_symmetry_Int_Tables_number   2
_chemical_formula_structural   Si2As
_chemical_formula_sum   'Si4 As2'
_cell_volume   126.89
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-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
  Si  Si0  2  0.0  0.23  0.25  1.0
  Si  Si1  2  0.0  0.45  0.08  1.0
  As  As2  2  0.0  0.15  0.62  1.0

Si Si Si Si As As