From atomic and molecular orbitals to chemical orbitals

In this work, we analyze the molecular orbitals (MO) one-electron functions of the Hartree-Fock (HF) model and the atomic orbitals (AO) of the Heitler-London (HL) and valence bond (VB) models. The complementarity of MO with AO orbitals has been evidenced with the recent Hartree-Fock-Heitler-London model. We propose a new and general one-electron function, the chemical orbital (CO) and the corresponding determinantal wave function, the chemical orbital wave function, ΨCO. We show that the ΨCO can be decomposed into a specific HF-HL function with ionic components, designated “adjoined HF-HL function” and that the HF-HL, HF, and VB wave functions can be derived from the ΨCO wave function. A single “adjoined HF-HL function” can realistically represent molecular systems from the united atom, to equilibrium distances, to dissociation; short linear expansions of “adjoined HF-HL functions” yield accurate nonrelativistic energies. Preliminary test computations with “adjoined HF-HL functions” are presented for the ground state of the H2 and LiH molecules © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008