Calculate the surface energy of the (100) face of a bcc material whose nearest-neighbor distance is 4 and whose cohesive energy between the atoms

Calculate the surface energy of the (100) face of a bcc material whose nearest-neighbor distance is 4 Å and whose cohesive energy between the atoms is ε = 1.5 eV/atom. Use the bond-breaking model and assume only nearest-neighbor interactions are important.