Bond ionicity of the halogen-silver interaction

The nature of the bonding between halogen atoms (F, Cl, and Br) and the Ag (111) surface has been investigated by analyzing ab initio Hartree-Fock wave functions for cluster models of the Ag surface and a halogen atom. Using a variety of criteria, we conclude that the bonding is ionic and that the halogen ionicity is essentially - 1. The measures of ionicity reported are (a) the expectation value of a projection operator which provides an indication of the total charge associated with the halogen atom, (b) the analysis of the dipole moment curve as function of distance, (c) the effect on the equilibrium bond distances of a uniform external electric field, and (d) the decomposition of the interaction energy into the sum of different contributions. This latter analysis shows that the bonding arises, almost entirely, from two effects: (1) the Coulomb attraction between the charged halogen and the metal and (2) the intraunit polarization of the metal and halogen subunits. © 1989 American Institute of Physics.