First-principles simulation of the encapsulation of molecular hydrogen in C120 nanocapsules

We investigate the encapsulation of hydrogen molecules in a C120 nanocapsule by using the density-functional-based tight binding (DFTB) method for geometry optimization and ab initio DFT approach for total energy calculations. It has been found that up to eight hydrogen molecules were encapsulated inside the C120 cage can form the stable complex. We show that for large numbers of encapsulated hydrogen molecules, some of them become chemisorbed on the inner surface of the cage. We found also that for nH2=54 the capsule side wall breaks and the mechanism of its breaking is studied by density-functional-based tight binding molecular dynamics (DF-TBMD) simulation thus this complex seems to be highly improbable. Our first-principles calculations predict that the hydrogen adsorptive capacity of C120 nanocapsules is higher than that of C60 fullerene. This demonstrates that C120 nanocapsules could be a promising material for energy storage.