Comments on the carbon cluster C60 and on its complexes with alkaline elements

We have analyzed in the Hartree–Fock approximation the carbon cluster C60 with a single‐zeta [(9,5)/(2,1)] basis set and a double‐zeta [(9,5)/(4,2)] basis set, the latter with and without 3d polarization functions. Estimates of the correlation energy correction were obained either using Becke's density functional theory or the Clementi–Chakravorty's electron–pair density approximation. The cluster's positive ion and singly and doubly charged negative ions have also been studied (doublets for C and C and singlet and triplet for C ) and computed both with a doublezeta basis set and defferent geometries or a double‐zeta plus polarization basis set. The geometries considered include the one obtained by quantum molecular dynamics using the Car–Parrinello approximation and two additional near this minimum. The computed ionization potential and electron affinity are in reasonable agreement with the experiments considering the basis sets adopted. A lithium, a sodium, or a potassium atom or the corresponding positive ions have been placed at the center of the cluster and have been shown to form stable complexes: C60Li+, C60Li, C60Na+, C60Na, C60K+, and C60K. In addition, preliminary data with a calcium atom are reported. Computations on model cluster C5, C6, and C9 are also reported to show that one needs large basis sets, extended use of polarization functions, and correlation corrections for quantitative results, more accurate than ∼5 kcal/mol per carbon atom, in the total energy, as in this work.