Ab initio coupled and uncoupled Hartree–Fock polarizabilities are computed for increasingly large oligothiophenes using the 3–21G, 6–31G**, 6–311G**, and the Sadlej medium-size polarized atomic basis sets. The comparison with experimental values highlights the large sensitivity of the measured polarizabilities with respect to working conditions. By extrapolating to the infinite chain limit the polarizability values of increasingly large oligomers, we compute the asymptotic polarizabilities per thiophene ring. The transversal, perpendicular, and longitudinal asymptotic coupled Hartree–Fock polarizabilities per thiophene ring are, using the 3–21G (6–31G**) atomic basis set, 49.7 (52.5), 15.2 (20.6), and 184.1 (190.0) a.u., respectively. Polythiophene is more polarizable than polydiacetylene, polyyne, and polysilane but less polarizable than polyacetylene which, in contrast to polythiophene, is much more difficult to process. Using a procedure which relates the polarizability and the topology of the one-particle states, the major contribution to the polarizability is attributed to π-symmetry crystalline orbitals located at the top of the valence bands, which look like an alternation of segments of the highest occupied crystalline orbitals of the all-trans and trans-cisoïd polyacetylene. However, a sizeable σ contribution comes from σ-conjugated segments formed by the sulfur atoms and their two adjacent carbon atoms.

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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 bandwidth 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.

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