Bond alternation, on-site Coulomb correlations, and solitons in polyacetylene

We explore the effect of including electronic on-site Coulomb correlations on the energy of solitons in polyacetylene within an unrestricted Hartree-Fock calculation for finite chains. For parameters characteristic of polyacetylene, we find that the conjugated non-magnetic ground state occurs only when the strength of the on-site electronic repulsion ($U$) is less than 4.66 eV. For this range of $U$ no significant changes occur in soliton energies and widths upon inclusion of on-site electronic repulsion.