A generalized Heitler-London theory of the chemical bond in H 2+

Abstract

The perturbation theory for the total energies of the 1sσg and 2pσu states of H2+ is reformulated in a manner which avoids problems resulting from symmetrization. First a new set of localized wave functions are defined and calculated from polarization perturbation theory. After symmetrization of these wave functions, a generalized Heitler-London energy, which can be expanded to all orders, is obtained. In second order the result agrees with the Murrell-Shaw Musher-Amos expression. An expansion of the expectation value of the energy is also carried out and provides similar results. Many symmetry-adapted perturbation results are obtained simply and directly from the present localized wave-function approach. The present theory suggests a novel interpretation of the terms contributing to the total potential energy and helps to rearrange them to give improved results. © 1991 American Institute of Physics.