Simulated structure and energetics of endohedral complexes of noble gas atoms in buckminsterfullerene

Classical molecular dynamics simulations were run for noble gas atoms confined within a buckminsterfullerene cage. The simulations indicated that all the endohedral complexes X@C-60 (X = He, Ne, Ar, Kr Xe) were stable relative to C-60 + X, with the Ar complex being the most stable. Except for the He complex, the minimum-energy configuration was with the endoatom at the geometric center of the cage. The minimum-energy position of the He atom in He@C-60 was off-center in a high-symmetry direction, but the energy lowering relative to a centered He atom was found to be small relative to the zero-point energy of the He atom within the cage. The simulations were checked by comparison of static energy computations with the fullerene fixed in its equilibrium geometry as determined alternatively from experimental data and from empty-fullerene calculations. The small differences between the alternative geometries were sufficient to cause significant quantitative changes in the computed binding energies but, except for predicting Xe@C-60 to be unstable, did not fundamentally alter our qualitative description of the results. (C) 2007 Wiley Periodicals, Inc.