Electron correlation in conjugated polymers

Summary form only given. Correlation effects on the band gap are studied to get the strength of electron interactions in conjugated polymers. In the presence of an additional electron or hole, the correlation induces a polarization cloud around the additional particle, which forms a polaron. For the excitation energy of a polaron, there is a competition between a loss of correlation energy in the ground state and a gain of polarization energy due to the scattering through the additional particle. The calculation has been done both for the Hubbard model and long-range interactions. For polyacetylene, we obtain the on-site repulsion U = 4.4 eV and the nearest-neighbor interaction V = 0.8 eV. The polarization effect of /spl sigma/ electrons and theoretical results on the effective interaction are discussed. The strength of effective interactions should depends on physical processes.