Point groups in three dimensions the finite subgroups of SO(3), are: the cyclic groups "C" (the rotation group of a canonical pyramid), the dihedral groups "D" (the rotation group of a uniform prism, or canonical bipyramid), and the rotation groups "T", "O" and "I" of a regular tetrahedron, octahedron/cube and icosahedron/dodecahedron. In particular, the dihedral groups "D", "D" etc. are the rotation groups of plane regular polygons embedded in three-dimensional space, and such a figure may be considered as a degenerate regular prism. Therefore, it is also called a "dihedron" (Greek: solid with two faces), which explains the name "dihedral group". The rotation group of
Two-dimensional liquid Two-dimensional liquid A two-dimensional liquid (2D liquid) is a collection of objects constrained to move in a planar or other two-dimensional space in a liquid state. The movement of the particles in a 2D liquid is similar to 3D, but with limited degrees of freedom. E.g. rotational motion can be limited to rotation about only one axis, in contrast to a 3D liquid, where rotation of molecules about two or three axis would be possible. The same is true for the translational motion. The particles in 2D liquids can move in a 2D plane, whereas the particles is a 3D