Numerical study of localized electronic states in disordered and doped conjugated polymers

Full text: The nature of electronic states in disordered and doped π-conjugated polymers is investigated. By means of a direct diagonalisation procedure (Lanczos algorithm) and use of Continued-Fractions Representation (CFR) we study, within the Su-Schrieffer-Heeger (SSH) model, numerically the effects of site and bond-type model impurities and solitons (geometrical defects in polyacetylene) on the electronic structure of trans-polyacetylene and polythiophene. We find that for energy eigenvalues equal to the impurity levels, electronic states are localised. Also, for each soliton there exists a localised electronic state which is situated at the midgap. Our results show (due to Pierels-distortion) that even in critical concentration (∼10%) of random distribution of solitons, the bandgap will not be closed