Spatial distribution of electron densities during optical excitation of C60.

We calculate the spatial distribution of the oscillating electron density for the low energy optical excitations in C(60), using ab initio time-dependent density functional theory. We contrast this with the unscreened free response of the Kohn-Sham eigenfunctions, in which the charge transfer is between hemispheres and the simple density oscillation patterns are very similar for electrons outside and inside the C(60) radius. In the screened case, the oscillation patterns involve charge transfer on the scale of interatomic distances. The exterior and interior densities play different roles in the oscillator strength and screening. Almost all of the dipole oscillation for optical absorption strength is from exterior electrons, a consequence of the superposition of π and σ electron oscillations. The lowest transition with appreciable strength is dominated by screening from π electrons.