Symmetry Operators for SHAPE
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In order to display symmetry operators in 3D mode, SHAPE needs to know the orientation of one member of each set. For Cartesian symmetry in a .SYM file, SHAPE requires the operators to be specified in "SYMOP" lines at the end of file. For example

SYMOP 1 0 0 2

indicates a 2-fold rotation axis parallel to x. The word "SYMOP is followed by the three Cartesian components of the axis and by the order of rotation.

SYMOP 1 0 0 -2

indicates a mirror plane perpendicular to x.

SYMGRP will write a SYMOP line for each symmetry operator which is actually entered, but it is is necessary to add generated operators manually. For example, for the icosahedral group derived as an example, SYMOP lines for the 5-fold and 3-fold axes are written by SYMGRP, but the 2-fold axes must be added. Only one, parallel to x (as above), y or z need be added. For the centric icosahedral group, the mirror planes must also be added, again as above.