  We investigate a range of possible materials containing the supermolecular
form of hydrogen comprising 13 hydrogen molecules arranged in an icosahedral
arrangement. This supermolecule consists of freely rotating 12 hydrogen
molecules in an icosahedral arrangement, enclosing another freely rotating
molecule. To date, this supermolecule has only been observed in a compound with
Iodane (HI). The extremely high hydrogen content suggests possible application
in hydrogen storage so we examine the possibility of supermolecule formation at
ambient pressures. We show that ab initio molecular dynamics calculations give
a good description of the known properties of the HI(H2)13 material, and make
predictions of the existence of related compounds Xe(H2)1, HBr(H2)13 and
HCl(H2)13, including a symmetry-breaking phase transition at low temperature.
The icosahedral (H2)13 supermolecule, remains stable in all these compounds.
This suggests (H2)13 is a widespread feature in hydrogen compounds, and that
appropriately-sized cavities could hold hydrogen supermolecules even at low
pressure. The structure of the supermolecule network is shown to be independent
of the compound at equivalent density.
