Before going over the description of a unit cell, it is important to give some definitions on basic concepts of crystallography from the view of CaRIne.

**Lattice and lattice points** : The lattice is classically defined as a group of points organised in space in such a way that each point has the same environment. The lattice is defined implicitly from the equivalent position generator associated to the unit cell.

**Motif** : The motif is the minimal unit that is repeated in the lattice. The motif associated to a unit cell counts three lists :

- list of
**atoms**, - list of
**bonds**, - list of
**polyhedra**.

**Unit cell** : The unit cell is the volume defined by the lattice vectors a, b and c. It is the minimal unit of volume that allows the construction of the total volume of a crystal (or grain) by unit cell juxtaposition (lattice translations). The three a,b and c lattice vectors define the unit cell reference frame. The unit cell is made up from a motif and an equivalent position generator.

All the objects defined in a unit cell are automatically searched and created (regarding to user defined criterions) in all the 3D graphic representations (unit cells, crystals, surfaces...) defined from this unit cell.