Evaluation Of The Molecular Linear Polarizability, Oscillator Strengths For Freec60, And Optical Constants For Films Ofc60

Ground-state local-density calculations have been performed to evaluate the free response of the wave-length dependent microscopic linear polarizability for theC60molecule using a sum-over-states approach. The influence of screening of the electromagnetic field was determined by applying external static electric fields in separate self-consistent-field calculations to evaluate the induced dipole moment. The polarizability calculated in the static limit was used to determine an effective screening parameter which was in turn used together with an RPA approach to calculate the wavelength dependent microscopic polarizability. Inclusion of screening was found to give an optical spectrum shifted about 0.4 eV from the experimentally determined absorption spectrum ofC60in solution. Furthermore, after introduction of Lorentz local-field factors, the evaluated dielectric function ε(ω) was compared with experimental data for films ofC60determined using ellipsometry in the 2–6 eV energy range and EELS techniques in the 0–30 eV energy range. The calculations compare reasonably well with experimental data except for a uniform shift of 0.4 eV in the 2–6 eV energy range and a shift of 2–3 eV in the 15–30 eV energy range.