Electronic structure and optical properties of bare and Li, Na, K and Ca coated C60 molecule

We study the electronic structure, geometric and low-energy optical properties of C60 and metal-coated M32C60, where M = Li, Na, K or Ca. The one-electron Kohn–Sham orbitals are used together with the RPA matrix to calculate the screened oscillator-strength distribution. The deep-lying levels in M32C60 have C60 character while those close to and above the Fermi energy have the character of the metallic M32 layer. Isolated alkali M32 shells are characterized by a double-peak structure in the range 1–3 eV, well below the π plasmon of C60 at about 6 eV. In M32C60 the M32 shell is coupled to C60, but the characteristic double-peak can still be identified.