Empirical interionic potentials for alkali halide molecules

A systematic study of families of empirical internuclear potential energy functions based on the Rittner potential is presented for alkali halide molecules, and comparison is made with recent binding energy and anharmonic constant data. It is concluded that the Rittner formalism, however parameterized, is incapable of consistent prediction of several molecular properties simultaneously, and that the potential seems to be failing to model some aspect of the detailed bonding of the molecule. Inclusion of a Gaussian form of repulsion potential in the model gives excellent agreement for the dissociation energies, but in general extreme care must be taken when applying empirical potentials of the Rittner form to more complex systems such as ionized molecules or clusters.