Space group diagrams

Laue symmetry is 2/m (disregarding the translational components of the 21-axis and the c glide), so the space group belongs to the monoclinic system. The simplified symbol P2 /c normally replaces the full symbol P 2 /c, and the old Schonflies symbol C A (the fifth space group derived from the point group C2h) is seldom used. 

In the following discussion, for simplicity we make use of the pair of symmetry diagrams that constitute a representation of space group P2 jc (No. 14) in International Tables for X-Ray Crystallography Volume /, as displayed in Fig. 9.3.4. 

Diagrams showing (a) the general equivalent positions and (b) die symmetry elements in space group P2 /c as presented in International Tables for X-Ray Crystallography Volume I. The bold numerals in the left figure are added for die purpose of discussion. 

The Wyckoff notation for a set of equivalent positions consists of two parts (i) the multiplicity M, which is the number of equivalent positions per unit cell, and (ii) an italicized small letter a starting at the bottom of the list and moving upward in alphabetical order. For a primitive unit cell, M is equal to the order of the point group from which the space group is derived for centered cells, M is the product of the order of the point group and the number of lattice points per unit cell. 

Note that in Fig. 9.3.4, diagram (b) can be derived from diagram (a), and vice versa, and either one is sufficient to represent the full symmetry of the space group. 

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The symbols are given at the upper comer of the space group diagrams. A fraction h attached to a symbol indicates two symmetry planes with height h and h + 1/2 above the plane of projection e.g. 1/8 stands for h — 1/8 and 5/8. No fraction means h — 0 and 1/2. 

Figure 1.7. Some graphical symbols used for symmetry planes in space group diagrams.

Figure 1.8. Some graphicai symbois used for symmetry axes in space group diagrams.

Figure 1.9. Space group diagrams for the low-symmetry triclinic space group PI (top) and the high-symmetry cubic space group Pm 3m (bottom).

Hydrogen/CalcOH http //www.ccpl4.ac.uk/ccp/ccpl4/ftp-mirror/nardelli/pub/ nardelli/ and GUI version within WinGX Hypertext Book of Crystallographic Space Group Diagrams and Tables http // img.chem.ucl.ac.uk/sgp/... 

Figure 3.11 Space group diagrams for planar group pi (a) symmetry elements (b) equivalent general positions (c) position of a triangular molecule motif (d-f) specification of the coordinates (x, y) of an atom...

Table 5.7 Graphical symbols used in space group diagrams...

Figure 5.2 Space group diagrams for space group No 74, P4 (a) symmetry elements (b) positions of motif generated by symmetry operations (c) asymmetric unit...

The space group diagrams are given in the following figure... 

The directions of the principal axes are given with respect to the crystallographic axes. Li(N2D5)S04 is orthorhombic with space group Pna2i, with lattice positions [Space Group Diagrams and Tables, http //img. chem.ucl. ac. uk/sgp/mainmenu.htm] ... 

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