Comments on the Space Groups

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All of the space group diagrams are drawn with the origin placed at the bottom left-hand corner of the diagram.

For the triclinic and monoclinic space group diagrams, the use of prime (') on the labels for the cell lengths (or angles) indicates that the length (or angle) is seen in projection on the XY plane of the screen. Similarly, the same comment applies to projections seen down the body-diagonal of the primitive rhombohedral unit cell.

For the orthorhombic space groups nos. 73 and 74, two-one axes are used in the long form of the space group symbols in order to emphasise the relationship of these space groups to P212121.

For many of the C- and F-centred tetragonal space groups, only a single quadrant has been drawn due to space limitations.

Only primitive unit cells have been drawn for the hexagonal space groups in contrast to the trigonal space groups where the H-centred cells are also shown.

For the cubic space groups, the diagrams show only the symmetry elements and not the symmetry equivalent positions of a point in an asymmetric position within the unit cell. Due to the limitations imposed by both space and resolution, for space groups nos. 203, 209-10, 216, 219-20, 225-8, and 230 only one quadrant of the unit cell is drawn. (For the F-centred unit cells, a single quadrant suffices since each quadrant appears the same in projection.) Due to the same limitation, the -4 axes are not shown for space groups nos. 225-6, and 229.

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