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The 2-fold screw axis consists of a rotation of 180° about an axis parallel to b, followed by a translation of ½ b in the b-direction. The screw axis passes through x = 0, z = ¼ (click "Screw Axis"). To apply the rotation operation of the screw axis, click "Rotate": This produces an "intermediate" molecule related to the original molecule by rotation. To translate this molecule ½ b, click "Translate ½ b":
The screw axis converts an atom at general location x, y, z to an identical atom at -x, ½ + y, ½ - z.
This "new" molecule is in a neighboring unit cell, to put it into the original cell, translate one unit cell length in the a-direction, click "Translate 1 0 0": These two molecules are related by a 2-fold screw axis that passes through x = ½ , z = ¼ . |
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