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

Abstract

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.

Confinement Resonances in Photoionization ofXe@C60+

“…This results in hybridization of the Ce atomic orbitals and a broadening of spectral features. Density-functional theory indicates that the Ce atom is located significantly off center in the C 82 cage [17], which would further mask any signatures of multipath interference [3].A nonreactive atom such as Xe is predicted to be centered within a C 60 cage [18]. A measurement of photoionization of Xe@C 60 in the energy range of Xe 4d ionization is therefore optimal for revealing evidence of confinement resonances, and for exploration of other multielectron phenomena associated with an atom in a cage.…”

Simulations of Xe@C60 collisions with graphitic films

“…Prior to carrying out the simulations, the endohedral Xe@C 60 complex and the graphite film were separately brought to minimum-energy configurations by kinetic energy drainage (so that the simulations were effectively run at zero temperature). The optimum position of the xenon atom was found to be in the geometric center of the fullerene complex, with the radius of the xenon-fullerene cage slightly larger (0.01 Å) than that of an empty cage [23]. Then, for each trajectory, the projectile, with its geometric center 20 Å away from the film, was asssigned an orientation and an initial velocity in the direction of normal incidence upon the graphite surface.…”

“…The potential also contains a cutoff factor that significantly limits interactions between nonbonded atoms. This factor contributes to a slight (3.4%) increase in fullerene cage radius when compared to experiment and quantum chemical theory [23]. The present studies involved endohedrally complexed Xe atoms; xenon was chosen because it increases the projectile mass and consequent ability to cause surface damage without significantly disturbing the bonding or structure of the fullerene cage.…”

“…Consequently, this study aims to complement previous results by providing statistically significant data regarding the types of collision scenarios and the impact energies at which they occur. Our investigation was carried out using a classical molecular dynamics code that has previously been implemented in studies of the structure and energetics of C 60 [23], as well as the surface-impact fragmentation of various fullerenes ranging from C 24 to C 240 [24]. The carbon-carbon interactions are modeled using the Tersoff potential [25], which contains parameterized three-body terms designed specifically for carbon allotrope simulations.…”

Role of exchange interaction in self-consistent calculations of endohedral fullerenes

“…In a number of papers it was supposed that in noble gas endohedral fullerenes A@C 60 a confined atom A is located in the center of the fullerene molecule [17,18,19] vibrating due to finite temperature [20]. In the present paper we assume that in case of Ar@C 60 these vibrations are insignificant at room temperature and consider Ar atom located in the center of the fullerene cage.…”