A face centered cubic unit cell contains atoms at all the corners of the crystal lattice and at the center of all the faces of the cube. The atom present at the face-center is shared between two adjacent unit cells and only 12 of each atom belongs to a unit cell. 2 Thus in a face centered cubic unit cell: a) 8 corners × 18 per corner atom = 8 × 18 = 1 atom b) 6 face-centered atoms × 12 atom per unit cell = 3 atoms Therefore the total number of atoms in a unit cell = 4 atoms

corners- 1 face 6*1/2=3 so finaly 1+3=4 atoms