First principles electronic structure calculations of the pentagonal dodecahedron (H2O)(20) (D-cage) and tetrakaidecahedron (H2O)(24) (T-cage), building blocks of structure I (sI) hydrate lattice, suggest that these can accommodate up to a maximum of 5 and 7 guest hydrogen molecules, respectively. For the pure hydrogen hydrate, Born-Oppenheimer molecular dynamics (BOMD) simulations of periodic (sI) hydrate lattices indicate that the guest molecules are released into the vapor phase via the hexagonal faces of the larger T-cages. The presence of methane in the larger T-cages was found to block this release, therefore suggesting possible scenarios for the stabilization of these coated clathrate hydrates and the potential enhancement of their hydrogen storage capacity. (C) 2011 Elsevier B. V. All rights reserved.