Dispersion interaction of conjugated molecules: One- and many-electron models

A scheme for calculating van der Waals constants C₆, C₈, and C₁₀ in terms of the full configuration interaction for π-shells is suggested. The required imaginary frequency dynamic polarizabilities are also investigated with one-electron schemes. The variational perturbation theory of the Hartree-Fock method considerably exaggerates the constant C_2l the conjugated variant of perturbation theory is preferable. The additive scheme for estimating the Σ-contribution allows one to calculate the energy of dispersion attraction in real conjugated systems, as demonstrated by semiempirical estimates of evaporation heat in butadiene, benzene, naphthalene, and phenylacetylene. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1029–1037, November–December, 1997. Original article submitted December 14, 1996.