State of hydrogen molecules confined in C₆₀ fullerene and carbon nanocapsule structures

The combination of PM3 semi-empirical method for geometry optimization, and ab initio DFT (density functional theory) for energy calculation, is used to study the configurations of hydrogen molecules at 0 K within the vacuum of C₆₀ fullerene and carbon nanocapsules. The obtained structural information including the molecular arrangement and structural state of the clusters of H₂ are mainly determined by two kinds of repulsive energies, namely that between the H₂ molecules and the wall of the spheroidal or capsule like carbon structure, and that between interacting H ₂ molecules. It is further established that the repulsive energy among the H₂ molecules is not purely a function of the number of encapsulated H₂, and there is a tradeoff between the two kinds of repulsive energies. © 2005 Elsevier Ltd. All rights reserved.