This estimate depends on an adequate sampling over a range of guest occupations, and should be most reliable for those clathrates where the simulation covered both fully saturated and completely empty structures. The heat of desorption does not vary substantially with temperature or pressure, why we report the average across all simulated temperatures and pressures q. The experimentally observable isosteric heat of adsorption is -q + RT . Our multipole-based force field for intermolecular interactions should be highly reliable, and has performed very well in the past . Some approximations are however necessary to be able to carry out a screening of so many structures. We have re-optimized the crystal structures after guest insertion, so the calculated lattice energies and lattice dynamics simulations do account for the relaxation of the host structure around the guest. However, this effect is not included in the grand canonical Monte Carlo simulations. The host structure is held fixed, and while this is computationally convenient, it neglects the fact that the host molecules also have thermal motion and that the unit cell expands and contracts with respect to temperature, pressure and the presence of guest molecules. Such effects are however not expected to greatly influence the results, since organic molecular crystals generally change in volume and lattice parameters by a mere 3% to 5% over the pressure-and temperature ranges we explore here . The changes in unit cell volumes in response to guest occupation are about as large .