Question

In a cubic unit cell, what is the contribution to the unit cell of the particle present at the centre of a face?

Answer 1

1. A particle present at the centre of a face in a cubic unit cell is shared by two adjacent unit cells because it is located on the common face between them. Therefore, each face-centred particle contributes half (1/2) of its volume to a single unit cell.
2. There are 6 faces in a cube. Each face-centered particle is shared by 2 neighboring unit cells (one on either side of the face). Hence, only half of the particle belongs to one unit cell.