The ideal gas approximation

As the model describes a single particle in a potential well, the H2$-$H2 interaction is introduced as empirical correction. For slowly varying potentials a simple correction for the behaviour of the physisorbed gas as a real gas can be made, as discussed above. The theoretical justification of the correction requires that the adsorption potential varies slowly at characteristic guest-guest interaction distances (Eq. 1.10), and across the entire adsorption volume (Eq. 1.11). The latter assumption is by far the most severe approximation of this treatment, and is likely to collapse completely for heterogeneous host materials and high guest densities. For such systems, the pressure-density relation within the accessible volume is strongly non-linear and the estimation of the guest non-ideality becomes meaningless.