Influence of libronic degrees of freedom on electronic properties of polyaniline

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Abstract
We investigate a one-band model with electron-libron coupling and a steric potential in order to discuss the influence of phenyl-ring rotations on the electronic properties of pernigraniline, the fully oxidized form of polyaniline. The T=0 ground-state phase diagram is mapped out, and it is shown that forward-scattering processes of electrons play an important role in the framework of this model. They lead to the possibility of a charge-separation ground state. Solitons are present due to a doubly degenerate ground state. The lack of particle-hole symmetry leads to some characteristic features of nonlinear excitations as a charge-density wave and a splitting of soliton and antisoliton energies. We also incorporate acoustic phonons into the model and analyze how important they are for pernigraniline. Some predictions following from a suitable choice of parameters are compared with quantum chemical results.