Our methodology uses grand canonical Monte Carlo moves combined with molecular dynamics (MD) trajectories in the (N, V, σa = 0, T ) ensemble, effectively constraining the volume while allowing the cell shape to fluctuate. In this way, the MD trajectories allow the framework to adapt to the fluctuating number of adsorbates resulting in flexiblehost adsorption isotherms, Nguest (N host , µ, σa = 0, T ; V ). These isotherms were calculated for a series of unit cell volumes between 40 nm 3 and 110 nm 3 with a spacing of 2 nm 3 . Subsequently, the flexible-host isotherms were used to construct the osmotic potential as Equation .