Can the 'van der Waals loop' vanish?. Effect of surface free energy

We have shown previously that the 'van der Waals loop' of the equation of state, an artifact which appeared in computer simulations for small-size systems, can be removed by enlarging the system size. In this Letter we argue that a large system size simulation is required only when the surface free energy of domains is large in the course of the phase separation, which usually occurs when the system is quenched deeply into a two-phase region. For a shallow quench, however, the 'loop' effect is not serious because of the small surface free energy of domains. We also show that such a shallow quench can also be achieved effectively by reducing the attractive part of intennolecular potential while retaining the repulsive part of the potential at the same system temperature.