Polarons and bipolarons in conjugated polymers: a density matrix renormalization group study

Relative stability between a polaron and a bipolarons in nondegenerate conj ugated polymers is investigated by the UHF and the density matrix renormali zation group (DMRG) methods in the extended Hubbard-Peierls model. Lattice distortion is optimized by using the Hellmann-Feynman condition. We show th at relative stability is very sensitive to electron correlation and that th e correlation effect stabilizes the bipolaron state in the case the on-site Hubbard U is much larger than nearest-neighbor V, Furthermore, a new mecha nism to stabilize bipolaron in strong V regime is suggested.