ABINITIO HARTREE-FOCK STUDIES OF THE BINDING-ENERGY OF A SOLITON TO A SODIUM COUNTERION IN DOPED TRANSPOLYACETYLENE

We have performed split valence ab initio Hartree-Fock calculations of the total binding energy, E(B), of charged solitons to donor impurities in doped trans-polyacetylene. The total energy is calculated for a system with the soliton pinned to the impurity and for a system where the soliton is isolated from the impurity. E(B) is taken to be the difference between the optimized total energies of these two systems. For a sodium counterion we obtain a total binding energy of E(B) = 3.18 eV. This value reduces to 2.25 eV when Moller-Plesset second-order perturbation corrections are included. The energy of the soliton level relative to the valence band edge is found to decrease by 0.22 eV in the presence of a sodium counterion, a result which correlates well with optical absorption data.