A scaled "one-electron Hamiltonian" model for open-shell LCAO-MO-SCF calculations

Abstract

An approximate technique of generating orthonormality-constrained one-electron orbitals for the description of open-shell systems is suggested. The "off-diagonal Lagrangian-multiplier problem" is circumvented by using a common potential for both the closed- and open-shell electrons. This common potential is generated by a scaling of the usual exchange potential of Hartree-Fock theory. The problem of choosing an appropriate scaling parameter (µ) is considered from both variational and perturbative points of view. The relationship of the present method with some other approximate open-shell theories is explored. The numerical results of computations carried out at the semiempirical MO level are presented in order to bring to light the dependence of computed molecular properties on the magnitude of the scaling parameter.