Energy spectrum and optical properties of C₇₄ fullerene within the Hubbard model

The energy spectrum and the optical absorption spectrum of C₇₄ fullerene are calculated within the Hubbard model with regard to strong Coulomb correlations. It is shown that, due to the strong correlations, the energy spectrum is split into two 5.732 eV wide Hubbard subbands. The gap between these subbands is the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and is equal to 1.268 eV. From the energy spectrum obtained, the optical absorption spectra of both pure fullerene and M@C₇₄ metal fullerenes, where M is a metal of valence 1, 2, 3, or 4, are calculated. For M = Ca, Sr, Ba, or Eu, the optical absorption spectrum at wavelengths λ < 1000 nm well agrees with experimental data.