Studies of the thermodynamic conditions for the existence of a stable liquid phase in square well fluids

The condition under which certain systems may not have a stable liquid phase, instead, sublime from the solid to the vapor phase has been the subject of investigations by many. Until recently, it used to be thought that any amount of attraction added to a short ranged repulsion would give rise to a liquid phase. However, computer simulations, theoretical, as well as experimental studies have showed that this is not the case. By use of Hyper-parallel tempering Monte Carlo (HPTMC) simulation, computer simulations were performed to obtain the liquid-vapor co-existence data for square-well (SW) fluid with variable interaction range with the view of determining the conditions where the liquid state will simply squeeze out. The interaction range (λ) which plays a significant role in giving rise to a liquid phase in the phase diagram was varied from 1.21 to 3.0. The results of the work clearly indicate that the range of temperatures for which the liquid is stable shrinks as the interaction range decreases. And for sufficiently short interaction ranges, the square-well fluid has no stable liquid phase with a threshold value of λ = 1.24.