To check the accuracy of this sampling technique, we compared it to our reference sampling, the Widom insertion with 100,000 cycles. Figure compares the enthalpy computed in the Voronoi sampling with the reference adsorption enthalpy (ground truth) -showing at the same time the largest cavity diameter for each porous framework. The correlation between the values of enthalpy is very good only for a restricted number of structures with enthalpy around -50 kJ mol -1 . For structures with higher enthalpy, the correlation starts to degrade, and becomes very poor for small-pore structures. For the points in purple, the largest cavity diameter is lower than the kinetic diameter of a xenon, the sampling of the Voronoi nodes is clearly insufficient. In addition, the accuracy loss on the other points (larger pores) can be explained by the fact that the pores are slightly bigger and the center of the pore is not a good approximation of adsorption site position anymore: the adsorption sites are actually closer to the pore surface than to the center of the pore. This conclusion is what prompted us to propose a new sampling scheme based on the molecular surface of the pore space, which we will detail in the next sections.