  Structure, stability and reactivity of clathrate hydrates with or without
hydrogen encapsulation are studied using standard density functional
calculations. Conceptual density functional theory based reactivity descriptors
and the associated electronic structure principles are used to explain the
hydrogen storage properties of clathrate hydrates. Different thermodynamic
quantities associated with H2-trapping are also computed. The stability of the
H2-clathrate hydrate complexes increases upon the subsequent addition of
hydrogen molecules to the clathrate hydrates. The efficacy of trapping of
hydrogen molecules inside the cages of clathrate hydrates depends upon the
cavity sizes and shapes of the clathrate hydrates. Computational studies reveal
that 512 and 51262 structures are able to accommodate up to two H2 molecules
whereas 51268 can accommodate up to six hydrogen molecules.
