issue with using Fix GCMC

Dear LAMMPS users,

I am using the lammps-16Mar18 version.
I am using multiple Fix GCMC in one script to control density of Argon in two sides of simulation box.
I am also using langevin thermostat to control the temperature of each side of simulation.
The simulation are performing at different pressure and temperature.

The fix gcmc works well for argon in liquid, vapor and also in the super-critical condition.

But, for the systems with the density near the critical density of argon, the fix gcmc cannot control the density of the system and add the argon atoms to the cell constantly and the density of the region(near the critical point) is increase as well.
I want to know the problem is related to functionality of the fix gcmc around the critical density or using multiple fix gcmc in one script.

I also attached the input script.
In this script,
in liquid region ( Temperature= 86.0 K, Pressure 111.66 atm, and density = 1.4 g/cm3) fix gcmc works well.
In the vapor region (Temperature= 164.65 K, Pressure 106.81 atm, and density = 0.86 gr/cm3) fix gcmc add the particle to this region constantly.

Many thank for your help.

Best Regards,
Farzin Rahmani

in.txt (3.1 KB)

No where in the documentation is it suggested that fix gcmc can be used to simulate critical phenomena.