Difference between revisions of "Pseudo symmetry"
From Online Dictionary of Crystallography
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| − | + | <font color="blue">Pseudo symétrie</font> (<i>Fr</i>); <font color="black">Pseudo simmetria</font> (<i>It</i>); <font color="purple">疑対称</font> (<i>Ja</i>) | |
| − | <font color="blue">Pseudo symétrie</font> (<i>Fr</i>); <font color="black">Pseudo simmetria | ||
Revision as of 15:37, 16 April 2015
Pseudo symétrie (Fr); Pseudo simmetria (It); 疑対称 (Ja)
A crystal space can in general be divided in N components S1 to SN. When a coincidence operation φ(Si)→Sj brings the i-th component Si to coincide with the j-th component Sj, for any i and j, φ is a symmetry operation of the space group.
Sometimes, φ brings Si close to, but not exactly on, the position and orientation of Sj: in this case the operation mapping Si onto Sj is not crystallographic but the linear and/or rotational deviation from a space group operation is limited. For this reason, it is preferable to describe the crystallographic operation φ as a pseudo symmetry operation.
Pseudo symmetry operations for the lattice play an important role in twinning, namely in the case of twinning by pseudomerohedry and twinning by reticular pseudomerohedry.