Mechanisms for thermal conduction in hydrogen hydrate.

Extensive equilibrium molecular dynamics simulations have been performed to investigate thermal conduction mechanisms via the Green-Kubo approach for (type II) hydrogen hydrate, at 0.05 kbar and between 30 and 250 K, for both lightly filled H(2) hydrates (1s4l) and for more densely filled H(2) systems (2s4l), in which four H(2) molecules are present in the large cavities, with respective single- and double-occupation of the small cages. The TIP4P water model was used in conjunction with a fully atomistic hydrogen potential along with long-range Ewald electrostatics. It was found that substantially less damping in guest-host energy transfer is present in hydrogen hydrate as is observed in common type I clathrates (e.g., methane hydrate), but more akin in to previous results for type II and H methane hydrate polymorphs. This gives rise to larger thermal conductivities relative to common type I hydrates, and also larger than type II and H methane hydrate polymorphs, and a more crystal-like temperature dependence of the thermal conductivity.