LOCALIZED AND EXTENDED STATES IN DOPED POLYANILINE - THE EFFECT OF BOND-LENGTH ALTERNATION

We present numerical studies of localization properties of oxidized and protonated disordered polyaniline. The calculations are performed on the single electron level, using Huckel theory for pi electrons. The spatial extension of the eigenstates at the Fermi energy is determined by a fast and accurate transfer-matrix scheme. The spatial extension of eigenstates diverges for a large degree of protonation, provided all bonds within the benzoid and quinoid can be described with the same set of tight-binding parameters. Localization effects become important for small degrees of protonation and in systems that show bond-length alternation in quinoid rings and aromatic bonds in benzoid rings.