MNDO Parameters for Helium: Optimization, Tests, and Application to Endohedral Fullerene—Helium Complexes

MNDO parameters for helium are derived from an optimization that employs only atomic and diatomic reference data. Comparisons with published high-level ab initio results indicate that MNDO correctly predicts the existence of covalently bonded helium compounds and normally reproduces the geometries of these small charged molecules reasonably well. Endohedral fullerene–helium complexes and the transition states for their formation are studied for C₆₀, C₆₀, and C₆₀²⁺. The calculated barriers are discussed and compared with those for the passage of helium through C₆H₆, C₆H₆⁺, and C₆H₆<sup>2+