Optical Excitations in Conjugated Polymers

We investigate optical absorption spectra and excitons in conjugated polymers from first principles. This is done by calculating the one-particle and the two-particle Green's function, including relevant many-body effects, and evaluating quasiparticle and optical excitations. Trans-polyacetylene and poly-phenylene-vinylene are studied as prototype long chain polymers. The electron-hole interaction gives rise to large exciton binding energies ( $\sim 1$ eV) and dramatically alters the optical spectra. The calculated exciton wave functions are very extended in real space.