Bound electronic states of the smallest fullerene C20− anion

Abstract

We report on high-level coupled-cluster calculations for the anion states of the smallest fullerene C₂₀. Using the state-of-the-art EA-EOM-CCSD method we revealed that the C₂₀⁻ anion has five bound electronic states at the C₂₀ neutral ground-state D_3d equilibrium configuration. These are two pairs of ²E_u and ²A_2u states and one ²A_1g state. The binding energies vary from 2.05 eV for the most bound ²E_u state to <1 meV for the ²A_1g state. An analysis in terms of radial and angular density distribution of the excess electron revealed that the two ²E_u/²A_2u pairs are valence-like states while ²A_1g corresponds to a super-atomic-like (SAMO) state. The valence states of the first ²E_u/²A_2u pair were found to be of p-type whereas those of the second pair are of hybrid sp-type. We have also applied a simple model to understand the binding of the excess electron in C₂₀⁻. The model confirms the existence of only one SAMO state of the s-type for C₂₀⁻. At the same time, it overestimates the number of the bound valence states of C₂₀⁻.