``Multiple-Scattering'' Model for Polyatomic Molecules

The ``multiple-scattering'' technique of determining energy bands in solids is modified for the problem of calculating bound one-electron eigenstates of polyatomic molecules. The computational simplicity and applicability of this method to molecules of arbitrary complexity are dependent on the adoption of a model Hartree—Fock Hamiltonian based on the Slater approximation to the exchange potential and on the assumption of truncated spherically averaged potentials. The composite wavefunctions are expanded in rapidly convergent partial-wave series around each atomic site. For molecules of moderate size, the calculations can easily be carried to self-consistency within the spherical approximation, and first-order perturbation theory can be applied to correct for the nonspherical components of the potential. Emphasis is placed on the advantages of this technique as a first step in calculating the theoretical electronic spectra of complex polyatomic systems.