We also investigate the relationship between the optimized tankage fraction of the adsorbed xenon storage systems and the gravimetric surface area (defined by the zero potential energy contour of a xenon probe adsorbate in the pores, computed in iRASPA ) of the corresponding nanoporous materials. Fig. shows that nanoporous materials that exhibit high gravimetric surface areas tend to have lower tankage fractions. Similarly, according to virtual screenings of MOFs, for hydrogen storage, MOFs with the highest gravimetric surface areas tend to give the highest usable capacity of hydrogen ; however, for methane storage, intermediate gravimetric surface areas are desirable .