If particles are present only in the corners it is called Primitive unit cells.
The smallest repeating unit of the crystal lattice is the unit cell, the building block of a crystal. A unit cell can either be primitive cubic, body-centred cubic (BCC) or face-centred cubic (FCC).
Primitive Cubic Unit Cell
The atoms in the primitive cubic unit cell are present only at the corners and every atom at the corner is shared among eight adjacent unit cells. Four unit cells are present in the same layer and four unit cells in the upper/lower layer. Thus, a particular unit cell has the only 18th of an atom and each small sphere represents the centre of a particle which occupies that particular position and not its size.