Theory of the excitonic effect in solid C60.

Abstract

In this paper a theory of the excitonic effect in solid ${\mathrm{C}}_{60}$ is presented. We first develop an empirical pseudopotential method to calculate the energy levels of the ${\mathrm{C}}_{60}$ molecule, which provides a good basis for the inspection of optical transitions in both the ${\mathrm{C}}_{60}$ molecule and solid ${\mathrm{C}}_{60}$. Then a theory is established to describe the characters of excitons in solid ${\mathrm{C}}_{60}$. It is found that excitons in solid ${\mathrm{C}}_{60}$ are intermediates between the Frenkel and Wannier types and the photoabsorptions in solid ${\mathrm{C}}_{60}$ are mainly due to the excitonic transitions. The dielectric function of solid ${\mathrm{C}}_{60}$ is calculated based on this theory and some relevant experimental results are discussed.