go back to : Crystallography :: 3D Modeling

Unit cell defintions

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.

Unit cell inspector window

All the properties of a unit cell are inspected via the inspector window. For example, it is possible to access to the motif or select the equivalent position generator of a unit cell from this inspector...

| Learn more

Equivalent positions generator

The lattice associated to a unit cell is defined from one of the seven crystalline systems, six unit cell parameters and one equivalent position generator (Bravais lattice or space group)...

| Learn more