Analysis of the polarizability and optical properties of C-60

The interaction between electromagnetic radiation and the C-60 molecule has been analysed by an evaluation of the low-energy part (less than or equal to 40 eV) of the linear response spectrum of buckminsterfullerene, C-60. Single-particle wavefunctions, determined from local-density ground-state calculations, were used for evaluation of dipole matrix elements which, combined in a sum-over-states approach, yielded wavelength-dependent free-response microscopic linear polarizabilities. Screening of the external electromagnetic held through the induced charge distribution was determined by applying external static electric fields in separate self-consistent held calculations and by evaluation of the induced dipole moment. The polarizability calculated in the static limit was used to determine an effective screening parameter for evaluation of the dynamic response. The inclusion of screening was found to give an optical spectrum in rather goad agreement with the corresponding experimentally determined spectrum of C-60, in the gas phase or solution, by absorption measurements, EELS or photoionization techniques. Furthermore, by the use of Lorentz local held factors, we find a similar agreement for the dielectric function epsilon(omega) determined from C-60 ellipsometry and EELS measurements. In the above cases, the shapes of the spectra are essentially reproduced except for a uniform shift of about 0.5 eV to the low-energy side in the region less than or equal to 10 eV and about 4 eV in the opposite direction in the region above 10 eV.