Electron interaction and soliton energy in conjugated polymer

The effect of e-e interaction on the creation energy of soliton in polymer has been extensively studied by using the Hubbard model. However, the polymer possesses wide bandwidth, which is even larger than the on-site repulsion U, then it canʹt be guaranteed that the Hubbard model is always suitable, since this model originates from the systems with narrow band. Actually the Hubbard model only contains the diagonal part of e-e interaction, for wide band system, the off-diagonal part of e-e interaction may have substantial impact. This paper goes beyond the Hubbard model by using a screened Coulomb interaction, which includes both diagonal and off-diagonal parts. Our calculation shows that the effect of e-e interaction on the creation energy of soliton is distinctly different from the result based on the Hubbard model, the physical reason cause this difference is analysed.