Molecular orbital perturbation theory II. Charge displacement and stabilization in conjugated molecules

This paper develops a method of investigating changes in the electronic structure of a molecule caused by a perturbation such as a substituent or the field of another particle. The method is based on a Hamiltonian including electron interaction. The total wave function for the perturbed molecule is written as a linear combination of approximate self-consistent molecular orbital functions for the ground and excited states of the unperturbed system . First- and second-order expressions for changes in energy and charge distribution are given which are generalizations of results previously obtained using an independent-electron model.