Ab initio study of hydrogen storage in water clathrates

The H2 occupancy in type-ll hydrogen clathrate hydrate is determined using ab initio quantum chemistry calculations. Free energies of association show that the small (D-512 ) cage is singly occupied while the large (H-512 64 ) cage favors four-fold occupancy. If volume and geometry were the only controlling factors, then occupancy of both cages would be significantly larger. Therefore, repulsive forces between guest hydrogen molecules and between guest hydrogen and host water molecules in the cages must play a significant role in determining the occupancy of water clathrates. Copyright © 2010 American Scientific Publishers.