Ab initio investigation of the electronic properties of planar and twisted polyparaphenylenes

Ab initio band-structure calculations are carried out on stereoregular polyparaphenylene at the Hartree-Fock level of approximation using the split-valence 3-21G basis set. We investigate the effects due to the torsion angle between adjacent phenyl rings upon the ionization energies and bandwith values, as well as upon the density of states and the uncoupled Hartree-Fock longitudinal polarizability per unit length. From the band-width values, it is inferred that solid polyparaphenylene is better represented by the 22.7° twisted structure, whereas the torsion angle of polyparaphenylene in the gas phase should be roughly 40°. As for polypyrrole, polyfurane, and polythiophene, the highest occupied crystalline orbital is the most contributing band.