Non-additivity of polarizabilities and van der Waals C6 coefficients of fullerenes

We present frequency-dependent polarizabilities and C-6 dipole-dipole dispersion coefficients for a wide range of fullerene molecules including C-60, C-70, C-78, C-80, C-82, and C-84. The static and dynamic polarizabilities at imaginary frequencies are computed using time-dependent Hartree-Fock, B3LYP, and CAM-B3LYP ab initio methods by employing the complex linear polarization propagator and are subsequently utilized to determine the C-6 coefficients using the Casimir-Polder relation. Overall, the C60 and C70 average static polarizabilities alpha(0) agree to better than 2% with linear-response coupledcluster single double and experimental benchmark results, and the C-6 coefficient of C-60 agrees to better than 1% with the best accepted value. B3LYP provides the best agreement with benchmark results with deviations less than 0.1% in alpha(0) and C-6. We find that the static polarizabilities and the C-6 coefficients are non-additive, and scale, respectively, as N1.2 and N2.2 with the number of carbon atoms in the fullerene molecule. The exponent for C-6 power-dependence on N is much smaller than the value predicted recently based on a classical-metallic spherical-shell approximation of the fullerenes. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795158]