Packing sticky hard spheres into rigid zeolite frameworks

We describe a procedure for estimating the packing of spheres into rigid zeolite frameworks. Our method accomplishes the packing by placing spheres inside the framework, assigning a short-range attractive potential to spheres, thus making them ‘sticky’, and minimizing the total interaction energy using simulated annealing techniques. By varying the size of the spheres we can estimate the useful accessible pore volume of various probe molecules. We observe that the packing deviates the most from the densest state when sphere diameters equal the diameters of the Delaunay circumspheres associated with the framework; that is, when sphere diameters perfectly match the diameters of pores and sidepockets in the framework. We tabulate the packing density for hard spheres corresponding to the inert gases helium, neon, argon, krypton, xenon and water for 176 known zeolite framework types.