Combination of two or three symmetry operators

Sy cluster, then I operator (Fig. 14.9) the I operator, located at a distance along the z axis perpendicular to the screw direction, generates centrosymmetric pairs of screw ribbons. The new structure can be optimized by rotation of the S ribbon as a whole around its own propagation axis. The c cell axis must be c = 4z° since the b cell axis was fixed during the Sy search, the new cluster is 

Unfortunately, there is no hope of systematizing these operations for all space groups and orientations of symmetry operators, so the computer code must contain a special section for each combination and desired space group. The most common and useful combinations of two symmetry operators are summarized in Table 14.5. A reader who cares to follow in detail all the manipulations shown in that table learns all there is to learn about the geometrical crystallography of organic compounds [10]. 

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