A DIM MODEL FOR SODIUM CLUSTER-IONS INTERACTING WITH A CHARGED CONDUCTING SPHERE

A diatomics-in-molecules (DIM) model for the energy, shape and charge distribution of metal cluster ions in the presence of a charged insula ted conducting sphere is presented. The electrostatic interaction betw een the sphere and the cluster-ion is introduced in a self-consistent manner which allows the sphere to be polarized by the ion and the ion by the sphere. This interaction appears in the diagonal elements of th e model Hamiltonian matrix in such a way that the lowest eigenvalue in cludes the correct electrostatic energy for the charge distribution in the ground state. The model is applied to the calculation of fusion b arriers for Na-2(+) and Na-3(+) ions. When both the charge distributio n and the geometric configuration of the cluster-ion are allowed to re lax freely, the energy as a function of distance from the sphere is ne arly the same as that calculated from the electrostatic energy alone, which implies that details of the molecular structure of the cluster-i on can be neglected in calculating fusion barriers from charge polariz ation alone. That the fusion barriers lie sufficiently far away from t he sphere so that the molecule does not dissociate under the influence of the Coulomb interaction confirms that it is meaningful to speak of two separate entities at the barrier position.