The exchange time constant, denoted as τ , will be discussed in a later section on simulation details. In principle, the value of τ defines how efficiently the control volumes maintain concentration and pressure equal to that of the reference bulk system. Each control volume can be maintained independently at a specific pressure or concentration, and this allows for two different simulation modes. Specifically, in the non-equilibrium studies (NE-DCVMD), we are interested in establishing a concentration gradient across the system and steady state flux across the membrane. In this case, pressure in the sink control volume is set to zero and the exchange step involves removing all the molecules present in the control volume at τ intervals. In the equilibrium setup, both control volumes are set to maintain the same pressure and composition. In this case, there are no gradients in pressure or concentration across the system and the final state of the system corresponds to thermodynamic equilibrium. The later setup, termed here Equilibrium DCVMD (E-DCVMD), allows us to study equilibrium concentration and density profiles in the membrane under specific conditions of pressure, temperature and composition of the bulk system.