On the other hand, the pore volume can be computed from the crystal structure. Here, we choose the geometrical pore volume, which is an upper limit to the probe accessible pore volume. It is intuitively defined as all volume inside the unit cell that is not occupied by the atoms of the framework (described as hard spheres with Bondi's van der Waals radii). We note that certain pore pockets in adsorbents can be inaccessible to the adsorbing molecule due to narrow connection channels, which is not reflected in the geometric pore volume.