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Complex polarization propagator method for calculation of dispersion coefficients of extended pi-conjugated systems: the C6 coefficients of polyacenes and C60.

The frequency-dependent polarizabilities and the C6 dipole-dipole dispersion coefficients for the first members of the polyacenes namely benzene, naphthalene, anthracene, and naphthacene as well as the fullerene C60 have been calculated at the time-dependent Hartree-Fock level and the time-dependent density-functional theory level with the hybrid B3LYP exchange-correlation functional. The dynamic polarizabilities at imaginary frequencies are obtained with use of the complex linear polarization propagator method and the C6 coefficients are subsequently determined from the Casimir-Polder relation. We report the first ab initio calculations of the C6 coefficients for the molecules under consideration, and our recommended value for the dispersion coefficient of the fullerene is 101.0 a.u.