Hydrogen trapped in Ben cluster cages: The atomic encapsulation option

► Small beryllium cluster cages can trap hydrogen atoms endohedrally starting from Be6. ► H@Be6 units can be merged together, preserving integrity. ► Such assemblies are metastable to release of H2 and stabilized by an energy barrier. ► Extended to a nanofoam material, such systems may enable a high storage capacity. ► Shapes and electronic properties of the Ben shells are modified by the H cores.