Effect of the shape of simulation box on the Van der Waals loop of a Lennard-Jones fluid

It is demonstrated that the Van der Waals loop appearing in the computer simulations almost vanishes by modifying the shape of the simulation cell even when small size systems are treated. After a long molecular dynamics simulation, it was found that the complete phase separation into vapor and liquid took place in the unstable region. The surface free energy of the interface between the liquid and vapor phases is suggested to be a major reason why the artificial loop has been observed in molecular dynamics simulations. We show that the loop depth diminishes as the box ratio of the simulation cell is enlarged.