Zwitterionic and Diradical Breathers in Trans-Polyacetylene

We study effects of the 7r electron Coulomb interaction on breathers in trans-polyacetylene utilizing the Pariser-Parr-Pople (PPP) model. Charged solitons with opposite charges and neutral solitons with antiparalleI'spins, respectively, have attractive interactions and make dynamical bound states of two kinds, zwitterionic and diradical breathers. We numerically simulate adiabatic lattice motions to demonstrate the breather oscillations. The zwitterionic and diradical breathers have different energies, spatial extents and oscillation periods but have similar oscillation patterns. They may explain the ionic and neutral excitations observed in the photoinduced absorption spectra of trans-polyacetylene. The zwitterionic breather may also explain the self-pinning 'of photogenerated charged solitons.