For low-pressure adsorption, a widely used characterization is the adsorption enthalpy ∆𝐻 ads , which describes the affinity of an adsorbate molecule with the internal surface of the porous framework. In theory, this value is derived from the continuous Boltzmann average of the interaction energies ℰ int of the adsorbate with the framework over the entire porous space, and this integral is calculated using a discrete summation over a set of well-chosen points 𝑖 (note that the -𝑅𝑇 term comes from the ideal gas approximation):