Excitonic states of poly(para-phenylene)

Using a recently developed phenomenological Hamiltonian of poly(para-phenyl ene) and the density matrix renormalization group approach, we investigate the transition from bound to unbound states. Energies and exciton correlati on functions of the lowest excited states are calculated. The lowest B-1(1u )- states situated below the charge gap are found to be bound excitons. The 2(1)A(g)(+) state, being unbound, represents a band threshold; the exciton binding energy is found to be 0.74 eV.