SKEDSOFT

Primitive and Non primitive cells:

A primitive cell is a minimum volume unit cell. Consider a bravais lattice (in two dimensions) as shown below:

We can imagine two ways of identifying the unit cell in this structure. One is, with a1 and b1 as the basis vectors in which case, the unit cell will be a parallelogram. Here four lattice points are located at the vertices. This is a primitive cell. Other one is with the basis vectors a2 and b2 which would make a rectangle for the unit cell. Here in addition to the 4 points at the corners, one lattice point is at the centre. This is a non primitive cell. Thus the area of the non primitive cell is an integral multiple of the primitive cell.