Neglect of the coupling of the guest motion and host vibrations

Another important characteristic of the models is that the host structure is frozen. In reality, the host system is not static and its vibrations may affect both the accessible volume and the interaction energy landscape, having a significant effect on the storage capacity. In the most severe cases of very small pore sizes, the so called breathing modes can even prevent hydrogen from accessing the nanostructure. Another example of the guest-host coupling where the vibrations of the host can not be neglected is found for H2 physisorbed to convex surfaces. In this case the vibrations may push the adsorbed guest molecules away[39]. Both effects are expected to be strongly temperature dependent.

In hydrogen storage applications, the large difference between the effective masses of the guest and the host phonons suggests that the effects of the coupling could be estimated adiabatically, using frozen phonon models. At least in the case of graphene slit pores, these effects are negligible near room temperature (see ref. Patchkovskii2007).