Structural properties of doped polyacetylene chains: A comparative theoretical investigation using Hartree-Fock, Møller-Plesset second-order perturbation theory, and density functional theory approaches

The effect of doping on the geometrical structure of polyacetylene chains containing up to 101 carbon atoms has been investigated theoretically by using the Hartree-Fock approach, the second-order Meller-Plesset perturbation theory as well density functional theory with the hybrid B3LYP exchange-correlation functional. In all cases, the transfer of charge associated with doping induces important geometrical modifications as a result of the large electron-phonon coupling characterizing these π-conjugated systems. The geometrical modifications are mostly described by variations of the bond length alternation following a hyperbolic tangent relation. For chains bearing a positive charge, the Hartree-Fock scheme overestimates the defect localization with respect to the Møller-Plesset scheme where the soliton spans a 36 CH unit region. On the other hand, the B3LYP approach predicts the soliton to be excessively delocalized. When a counterion is added, the soliton defect is more localized. The soliton width goes from 5 ± 2 CH units when the counterion is a Li atom to 9 ± 2 CH units when it is a Cl atom. Moreover, in the presence of a counterion, the three approaches provide much similar bond length alternation and charge distribution patterns.