Collective effects in atomic collisions - I. Constrained Hartree-Fock approach for diatomic systems

As a first step towards a collective treatment of charge flow in atomic collisions, we construct ab initio potential energy surfaces as a function of the internuclear distance and the charge asymmetry between the two atomic species. To this end, the charge asymmetry off its stability value for a given nuclear separation is imposed upon the system by a suitable constraint within a two-centre Hartree-Fock calculation. Energy surfaces are presented for the systems LiH, HF, LiF, and CO. This representation offers a conceptual framework for visualising ionic or covalent molecular states and trajectories describing charge-changing collisions.