screw axis

A symmetry element of the crystallographic space group. When the whole crystal is rotated by a certain angle(180°, 120°, 90°, 60°) with respect to an axis and successively translated along the axis by a length of 1/2, 1/3, 1/4 or 1/6 of the crystal unit-cell, the translated crystal can be equivalent to the original crystal. In this case, this axis is called "screw axis." The screw axes are denoted by 2₁,3₁,3₂,4₁,4₂,4₃,6₁,6₂,6₃,6₄,6₅.

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