Schottky defect energies in CsCl structure type crystals

The Schottky defect formation energies (h s ) of seven CsCl structure crystals have been calculated, following the Mott and Littleton method, considering the second neighbour repulsions and the van der Waals interactions explicitly. The computed h s values (in eV) for CsCl, CsBr, CsI, TlCl, TlBr, NH 4 Cl and NH 4 Br are 1.860, 1.744, 1.407, 1.269, 1.204, 1.205 and 1.171 respectively. The results indicate that with a satisfactory model of cohesive parameters, the Mott and Littleton procedure yields reliable estimates of defect energies which are compatible with experiments.