data_global _chemical_name_mineral 'Sederholmite' loop_ _publ_author_name 'Wyckoff R W G' _journal_name_full 'Crystal Structures' _journal_volume 1 _journal_year 1963 _journal_page_first 85 _journal_page_last 237 _publ_section_title ; Second edition. Interscience Publishers, New York, New York Note: ideal nickel arsenide structure ; _database_code_amcsd 0011582 _chemical_formula_sum 'Ni Se' _cell_length_a 3.6613 _cell_length_b 3.6613 _cell_length_c 5.3562 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 120 _cell_volume 62.181 _exptl_crystal_density_diffrn 7.352 _symmetry_space_group_name_H-M 'P 63 m c' loop_ _space_group_symop_operation_xyz 'x,y,z' '-x,-x+y,1/2+z' 'x-y,x,1/2+z' '-y,-x,z' '-y,x-y,z' 'x-y,-y,1/2+z' '-x,-y,1/2+z' 'x,x-y,z' '-x+y,-x,z' 'y,x,1/2+z' 'y,-x+y,1/2+z' '-x+y,y,z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z Ni 0.00000 0.00000 0.00000 Se 0.33333 0.66667 0.25000