Effects of electron-electron interaction on the band structure in polydiacetylenes

The ground-state band structure of polydiacetylenes is theoretically studie d with the extensional Su-Schriffer-Heeger model supplemented by electron-e lectron interactions. The results show the following. First, the interval o f valence bands (conduction bands) increases because of the electron- elect ron interactions. Second, the effect of the on-site Coulomb energy (U) is d ifferent from that of the nearest neighbor Coulomb repulsion (V); the compe tition between U and V shows that U makes the bandwidth narrower and the ga p broader, whereas V makes the bandwidth broader and the gap narrower. Ther e is a critical value of UN. Third, the whole band width (E-omega) decrease s when the UN ratio is less than 1.0 and increases when the UN ratio is gre ater than 1.0 at V = 2.0 eV. Thus, the ground-state band structure is sensi tive to the UN ratio. The results also show that electron-electron interact ions can play an important role in the band structure of polydiacetylenes. (C) 2000 John Wiley & Sons, Inc.