For each aligned cage molecule, we overlay a regular, g × g × g grid of points (g = 50) that span 40 Å in each dimension, centered at the center of mass of the cage. The dimension of the [-20 Å, 20 Å] 3 cubic grid of points was chosen as the smallest to encompass all atoms of all the cages. The 3D porosity image of a cage is then a 3D array; element (i, j, k) is 0 if grid point (i, j, k) is classified as void and 1 otherwise.