Difference between revisions of "Asymmetric unit"
From Online Dictionary of Crystallography
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==See also== | ==See also== | ||
*[[Unit cell]] | *[[Unit cell]] | ||
| + | *Illustrations of the asymmetric units of the 230 space groups can be obtained on this [http://http://cci.lbl.gov/asu_gallery/ link] | ||
*Section 2.2.8 in the ''International Tables for Crystallography'', Volume A | *Section 2.2.8 in the ''International Tables for Crystallography'', Volume A | ||
[[Category:Fundamental crystallography]] | [[Category:Fundamental crystallography]] | ||
Revision as of 13:32, 27 August 2011
Unité asymétrique (Fr). Unità asimmetrica (It). 非対称単位 (Ja).
An asymmetric unit of a space group is a simply connected smallest closed part of space from which, by application of all symmetry operations of the space group, the whole space is filled. This implies that:
- mirror planes must form boundary planes of the asymetric unit;
- rotation axes must form boundary edges of the asymetric unit;
- inversion centres must either form vertices of the asymetric unit or be located at the midpoints of boundary planes or boundary edges.
These restrictions do not hold for screw axes and glide planes.
The term "aysmmetric unit" does not mean that this region has an asymmetric shape. In mathematics it is called fundamental region or fundamental domain.