Stabilization of the C20 Cage by Encapsulation of H+ and He2+ Ions

It is shown by ab initio calculations using secondorder Møller-Plesset perturbation theory and 6-31g, aug-cc-pVDZ and aug-cc-pVTZ basis sets and coupled cluster singles, doubles and perturbative triples method with the 6-31g basis set, that it is possible to stabilize the cage structure of the smallest fullerene C₂₀ by encapsulating small cations like H⁺ and He²⁺. While the latter stabilizes the cage structure by charge transfer, the former prefers to form a covalent linkage with the carbon atoms.