Static polarizabilities of doubly charged polyacetylene oligomers: basis set and electron correlation effects

Abstract

Abstract Ab initio calculations, carried out with different basis sets, for the static longitudinal linear polarizability, αL, and second order hyperpolarizability, γL, of small doubly charged polyacetylene (PA) chains, are presented. The polarizabilities were calculated using the Hartree–Fock (HF) method while the electron correlation effects were included through the second-order Moller–Plesset perturbation theory (MP2). Positively and negatively charged bipolarons were studied. The results obtained for positive and negative chains show that the ionization state effect decreases more rapidly, as the chain length is increased, for αL than for γL. For both types of charged chains, the incorporation of the electron correlation increases the αL and γL values, as compared to the HF values. A comparison between the results obtained using the standard 6-31G basis set and augmented versions of this set, obtained by the addition of diffuse and polarization functions, shows that 6-31G basis set does not provide a good description of the negative chains studied here and that the addition of extra diffuse functions on the basis set is needed in order to obtain reliable estimates for polarizabilities, specially for γL.