In mathematics, a layer group is a three-dimensional extension of a
wallpaper group, with reflections in the third dimension. It is a
space group with a two-dimensional lattice, meaning that it is symmetric over repeats in the two lattice directions. The symmetry group at each lattice point is an axial
crystallographic point group with the main axis being perpendicular to the lattice plane.
Table of the 80 layer groups, organized by
crystal system or lattice type, and by their point groups
:
Correspondence Between Layer Groups and Plane Groups
The surjective mapping from a layer group to a
wallpaper group (
plane group) can be obtained by disregarding symmetry elements along the stacking direction, typically denoted as the z-axis, and aligning the remaining elements with those of the
plane groups.
The resulting surjective mapping provides a direct correspondence between layer groups and
plane groups (
wallpaper groups).
See also
*
Point group
*
Crystallographic point group
*
Space group
*
Rod group
*
Frieze group
*
Wallpaper group
References
{{Reflist
External links
Bilbao Crystallographic Server under "Subperiodic Groups: Layer, Rod and Frieze Groups"
Nomenclature, Symbols and Classification of the Subperiodic Groups, V. Kopsky and D. B. Litvinby Frank Farris. He constructs layer groups from wallpaper groups using negating isometries.
Euclidean symmetries
Discrete groups