gas permeability through mixed matrix polymeric membrane?

Hello all,
i have been simulate a PDMS polymeric membrane which loaded by fumed silica and POSS nanomaterials.During simulation after i used adsorption and then forcite module (to find permeability of H2 from this membrane), i found diffusivity coefficient with MSD,but some of my results in high pressur were so far from other results,how can i find permeability of H2 from this membrane by materials studio? can anybody give me full help to simulate this system?