BULK PROPERTIES FROM FINITE-CLUSTER CALCULATIONS .6. A FINITE-SIZE PERTURBATION-THEORY FOR THE HARTREE-FOCK ENERGY OF LINEAR OLIGOMERS

A finite-size perturbation theory that expresses the total Hartree-Fock energy and the orbital energies of a finite nonmetallic linear oligomer composed of N identical unit cells as power series in nu = N-1 is derived. The coefficients for the first three terms of these series are evaluated explicitly through the first order of the Hartree-Fock formalism. The form of the uncoupled second-order contributions is discussed. The resulting expressions contain infinite sums involving the Wannier orbitals of the bulk polymer. The presence of nonanalytic terms in the expansion is also commented upon.