Currently I am working a molecular simulation to determine phases of an argon NPT ensemble using Lennard Jones potential. Mainly I use the radial distribution function to determine solid, liquid, or vapor state by investigating the structure.
A problem comes in when I notice that there are some states which should be in vapor form that exhibit the radial distribution function of liquid (showing a widen peak). I surmise that there may be due to the high density gas especially above the critical point.
Is there any way to decisively differentiate the liquid and vapor phase?