Collective charge density fluctuations and nonlinear optical responce of C60

The absolute magnitute of the optical susceptibility χ(3) for C60 and its frequency dispersion are calculated using the Pariser—Parr—Popl (PPP) model by deriving equations of motion for the single electron density matrix and solving them using the time-dependent Hartree—Fock procedure. Collective charge density fluctuations induced by the radiation fields are shown to provide the mechanism for the linear and the nonlinear optical response. The insight provided by the present real space picture allows the direct comparison with linear conjugated polyenes.