Local density functional study of the structural and electronic properties of C60 and XC60 (X=K, Rb, Cs)

Results of first principles local density total energy and atomic force calculations carried out for free C₆₀ and XC₆₀ (X=K, Rb, Cs) molecular clusters are reported. The optimization of the geometry results in the bond lengths between adjacent carbon atoms being 1.387 and 1.445 Å, which are in very good agreement with the latest X-ray diffraction values. Energy levels, charge distributions, and wavefunction characteristics are obtained and discussed. The results for C₆₀ are in very good agreement with recently measured photoemission energy distribution curves (EDC) for the valence band states. The highest occupied molecular orbitals (HOMO) are found to be fully occupied H_u states and are 1.7 eV below the lowest unoccupied molecular orbitals (LUMO) which are of T_1u symmetry. Similar results obtained for the XC₆₀ clusters show that rigid-band-like behavior is found in the electronic structures after putting an alkali atom at the center of a C₆₀ ball. In each case, the alkali atom is almost fully ionized with the transferred electron distributed over the surface shell of C₆₀; the center region of the ball has very low charge density.