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.