Multiconfigurational SCF approach for high-symmetry molecules and its applications to fullerene trianion

Abstract

A symmetry-adapted multiconfiguration self-consistent field MC SCF approach aimed at calculations of high-symmetry molecules is proposed. The selfconsistency procedure applicable to the molecular terms of any symmetry and multiplicity is developed. It holds the symmetry transformation properties of varied molecular orbitals, thus taking advantage of the relationships within the set of two-electron integrals through molecular invariants. For orbital optimization, a unified coupling operator is constructed on the basis of the pseudosecular method providing for efficient convergence to energy minimum. Based on the group-theory technique, computer codes have been developed for straightforward determination of the invariant expansions for Ž . two-electron integrals and configuration interaction CI matrix elements. Calculated in this way, the expansion coefficients are presented for the three-electron states that originate from joint t and t shells of an icosahedral fullerene C , the case important for lowest quasi--electronic states of C 3y are discussed. ᮊ

Electron Correlation Effects in Multicharged Ions of Icosahedral C60Fullerene

“…We take full advantage of C 60 high symmetry basing on the molecular-invariant theory. According to [10], the elements of H [k] are determined by simple expressions that are linear combinations of molecular invariants defined via a few molecular integrals. Only the integrals depend on the specific parameters of the model whereas the coefficients are defined only by the symmetry and multiplicity of a molecular state.…”

“…To get comparable results, the same model Hamiltonian and unified approximations for wave functions are used in the calculations of many-electron states. We apply the configuration-interaction (CI) approach using the molecular-invariant technique [10,11] to take full advantage of the high fullerene symmetry. This approach provides a unified treatment of the different C 60 charge forms, and the results easily tabulated for different potentials are equivalent to those obtained within the straightforward CI approach.…”