We study the extent to which finite polyenes and polyacetylene can be described by the extended Peierls-Hubbard Hamiltonian (ePHH) in an internally consistent manner. Using Lanczos exact diagonalization methods (LEDM) on small systems, coupled with a novel boundary condition (b.c.) averaging technique, we investigate the excited state spectra of these models for the finite oligomer analogs of trans-polyacetylene, (CH)x. We search for sets of parameters describing the electron-phonon (e-p) and electron-electron (e-e) interactions which are consistent with all available experimental data on these systems, including the optical gap and bandwidth, the 21 Ag state, longitudinal optical phonon frequency ωLO2, triplet excitations, and the optical absorptions assigned to charged and neutral solitons and to polarons. We conclude that the e-p coupling is substantially weaker than that suggested by purely e-p models and that the e-e interaction parameters are in the intermediate coupling regime (U ∼ 2.5t0), consistent with values deduced from the finite polyenes.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Materials Chemistry
- Polymers and Plastics