DMRG studies of the 1B exciton binding energy and 1B/2A crossover in an extended Hubbard-Peierls model

Using a symmetrized density matrix renormalization group formulation, we have investigated the electronic binding energy (Eb) Of the lowest optically allowed exciton (1B) and the crossover behavior of the 1B/2A states within an extended Hubbard-Peierls model (with parameters U, V, and delta) for conjugated polylner chains with N=80. The E-b value is found to be around 0.1 eV for polyacetylene and 0.22-0.45 eV for PPV when considering a realistic range of parameters. The 1B/2A crossover behavior is investigated for a wide range of parameters