POLARONIC EXCITATIONS IN THE DOPED POLYACENE

The polyacene as two coupled chains of transpolyacetylene has been stu died based on an extended SSH-Hubbard model. The dimerized displacemen t u(0) is found to be similar to the case of trans-polyacetylene, and equals to 0.04 Angstrom. The energy-band gap is 0.38 eV, in agreement with other authors. In particular, we have considered some cases where polyacene is doped with one and two donor electrons. In the case of d oping with one electron, a polaron spreading over two chains has been found; in the case of doping with two electrons having different spins , a stable bipolaron has been obtained, which is different from the on e of transpolyacetylene; in the case of doping with two electrons havi ng the same spins, two stable polarons which spread over two chains ha ve been found. The bound electronic states corresponding to these case s are obtained.