Interionic potentials for the alkali metal chlorides

Various models for the interionic potential in the alkali metal chlorides have been examined. The parameters in these potentials have been determined by fitting the equilibrium, elastic and dielectric properties of each substance. The potentials are compared graphically with each other, with the theoretically derived potentials of Kim and Gordon (1,2) and with a potential derived earlier by Catlow, Diller, and Norgett (3) by fitting the properties of sixteen alkali halides simultaneously. Intrinsic defect properties of the four chlorides have been calculated from these potentials. The results show that while it is possible to derive adequate two-body potentials for these salts from fitting their bulk properties, it is concluded, as found earlier by Catlow, Diller, and Norgett (3), that such potentials need to have the anion–cation interaction hardened by neglecting completely the Van der Waals interaction between nearest neighbours. Inclusion of non-central forces does not improve the potential, as judged by the criterion of the results of defect calculations.