First-principle calculations of the electronic properties of poly(p-phenylenevinylene), polyacetylene, and their derivatives

Results of density-functional studies of the electronic properties of poly( p-phenylene-vinylene) (PPV) and polybutadiene are presented. The calculatio ns were performed using a single-chain, full-potential, linearized muffin-t in orbital (LMTO)-based method. In particular, we analyze the effects on th e electronic properties due to the addition of substituents to the vinylene Linkage. As substituents, we concentrate on cyano and amine groups. It is found that these groups induce large changes in the band structures of thes e systems, particularly of the bands closest to the Fermi level. Further, t he effects on the band gap and on the total energy due to the bond-length a lternation of the polymer backbones, are analyzed both for unsubstituted an d substituted polybutadiene. It is found that both properties depend sensit ively on both the substituents attached to the chain and on the precise str ucture of the polymer. The substituents lead to overall redistributions of the electrons and, in particular, the disubstituted PPV is found to have a large dipole moment perpendicular to the polymer axis. For disubstituted po lybutadiene we find a stronger C-C bond-length alternation than for the uns ubstituted compound (polyacetylene), and the results for this compound indi cate that the band gap of substituted and unsubstituted PPV depends strongl y on the bond-length alternation. (C) 1999 Elsevier Science B.V. All rights reserved.