Icosahedral (H2)13 supermolecule

We investigate a range of possible materials containing the supermolecular form of hydrogen comprising 13 H2 molecules arranged in an icosahedral arrangement. This supermolecule consists of freely rotating 12 H2 molecules in an icosahedral arrangement, enclosing another freely rotating H2 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 we make predictions of the existence of the related compounds Xe(H2)13, 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.