The polaron and bipolaron states of poly(phenylene vinylene)

We utilize the Pariser-Parr-Pople model for poly (phenylene vinylene) (PPV) and take into account the realistic lattice structures of PPV considering the electron-electron and the electron-phonon interactions so that we can e xpose the subtle electronic and the lattice structures of PPV. We find that the lattice deformation is mainly in the vinylene group, and we also discu ss the spin density waves of polaron and the charge density waves of polaro n and bipolaron. The spin density wave is modulated by charge density wave. The competition between polaron and bipolaron are studied. We find that wh en the electron-phonon interaction lambda <0.21 and the intersite electron- electron interaction v is comparably small, v favors the polaron. When lamb da >0.21, v favors the bipolaron. (C) 2001 American Institute of Physics.