Optical excitations in conjugated polymers

We investigate optical absorption spectra and excitons in conjugated polyme rs from first principles. This is done by calculating the one-particle and the two-particle Green's function, including relevant many-body effects, an d 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 ilar to 1 eV) and dramatically alters the optical spectra. The calculated e xciton wave functions are very extended in real space.