Effects of electron correlation on doping in conjugated polymers — a study of the SSHH and BKH models using the DMRG method

We adopt the Su-Schrieffer-Heeger (SSH) Hamiltonian supplemented by a Hubbard term, which we call the SSHH model, for systems with a degenerate ground state, and the Brazovskii-Kirova (BK) Hamiltonian supplemented by a Hubbard term (BKH model) for systems with a nondegenerate ground state, to study the effect of electron correlation on doping in conjugated polymers. The density matrix renormalization group (DMRG) technique developed by White has proved to be a very powerful tool for treating low-dimensional systems with strong correlation. This method is applied to the above models. We first study the metal-insulator transition within the SSHH model. With the BKH model, we investigate the formation of bipolarons versus separated polarons in a nondegenerate system. Optical signatures of polarons are also calculated.