Variable-screening model for the quasimolecular treatment of ion-atom collisions

An effective single-electron potential is proposed which is appropriate for a realistic description of the electronic motion in quasimolecular systems formed in near-adiabatic ion-atom collisions. The potential is represented as a sum of two spherical potentials, each centered about one of the colliding nuclei. For finite internuclear distances, these potentials are obtained by smoothly interpolating the screening parameters of suitable atomic potentials (Thomas-Fermi or phenomenological potentials) between the united-atom and separated-atom limits (''variable-screening model''). The use of phenomenological potentials entail a great accuracy in describing the atomic states and opens up the possibility of treating ionized quasimolecular systems which were hitherto inaccessible to molecular-orbital Hartree-Fock calculations. Molecular correlation diagrams calculated from the variable-screening model for various neutral and ionized systems are presented. For the neutral cases the agreement with the results of Hartree-Fock calculations is surprisingly good. The scaling properties of the variable-screening model are discussed