Electron correlation in the excited state of conjugated polymers

Correlation effects in the excited state of conjugated polymers are investigated. 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 the correlation energy and a gain of the polarazation energy. The calculation on correlation effects of the band gap has been done for both the Hubbard model and long-range interactions.