Molecular crystal approach for pi-conjugated polymers: from PPP Hamiltonian to Holstein model for polaron states

Abstract

Starting from the $\pi$-electron Pariser-Parr-Pople (PPP) Hamiltonian which includes both strong electron-phonon and electron-electron interactions, we propose some strongly correlated wave functions of increasing quality for the ground state of conjugated polymers. These wavefunctions are built by combining different finite sets of local configurations extended at most over two nearest-neighbour monomers. With this picture, the doped case with one additional particle is expressed in terms of quasi-particle. Thus, the polaron formation problem goes back to the study of a Holstein like model.