| Pccn | D2h10 | mmm | Orthorhombic  |
| No. 56 | P21/c21/c2/n | Patterson symmetry Pmmm | |
Origin at -1 on 1 1 n
| Asymmetric unit | 0 ≤ x ≤ 1/4; 0 ≤ y ≤ 1; 0 ≤ z ≤ 1/2 |
Symmetry operations
| (1) 1 | (2) 2 1/4, 1/4, z | (3) 2(0, 1/2, 0) 0, y, 1/4 | (4) 2(1/2, 0, 0) x, 0, 1/4 |
| (5) -1 0, 0, 0 | (6) n(1/2, 1/2, 0) x, y, 0 | (7) c x, 1/4, z | (8) c 1/4, y, z |
Generators selected (1); t(1, 0, 0); t(0, 1, 0); t(0, 0, 1); (2); (3); (5)
Positions
| Multiplicity, Wyckoff letter, Site symmetry | Coordinates | Reflection conditions | |||||||||||
| General: | |||||||||||||
|
| 0kl : l = 2n h0l : l = 2n hk0 : h + k = 2n h00 : h = 2n 0k0 : k = 2n 00l : l = 2n |
| Special: as above, plus | |||||||||
|
| hkl : l = 2n | |||||||
|
| hkl : l = 2n | |||||||
|
| hkl : h + k, h + l, k + l = 2n | |||||||
|
| hkl : h + k, h + l, k + l = 2n |
Symmetry of special projections
| Along [001] c2mm a' = a b' = b Origin at 1/4, 1/4, z | Along [100] p2mg a' = b b' = 1/2c Origin at x, 0, 0 | Along [010] p2gm a' = 1/2c b' = a Origin at 0, y, 0 |
Maximal non-isomorphic subgroups
| I | [2] Pc21n (Pna21, 33) | 1; 3; 6; 8 | |
| [2] P21cn (Pna21, 33) | 1; 4; 6; 7 | ||
| [2] Pcc2 (27) | 1; 2; 7; 8 | ||
| [2] P21212 (18) | 1; 2; 3; 4 | ||
| [2] P121/c1 (P21/c, 14) | 1; 3; 5; 7 | ||
| [2] P21/c11 (P21/c, 14) | 1; 4; 5; 8 | ||
| [2] P112/n (P2/c, 13) | 1; 2; 5; 6 |
| IIa | none |
| IIb | none |
Maximal isomorphic subgroups of lowest index
| IIc | [3] Pccn (a' = 3a or b' = 3b) (56); [3] Pccn (c' = 3c) (56) |
Minimal non-isomorphic supergroups
| I | [2] P4/ncc (130); [2] P42/ncm (138) |
| II | [2] Aema (Cmce, 64); [2] Bmeb (Cmce, 64); [2] Cccm (66); [2] Ibam (72); [2] Pccb (a' = 1/2a) (Pcca, 54); [2] Pcca (b' = 1/2b) (54); [2] Pmmn (c' = 1/2c) (59) |
