Settings of GEMC-NVT simulation of water, hard to reach eqilibrium

[qqlovekerry]

Hello,
I am trying to do GEMC-NVT simulations to obtain the vapor saturation pressure of water at different temperatures. I found an example in the Examples/GEMC/Methane folder for methane. I modified the input file a little bit for simulation of water.
I added the charge_style since oxygen and hydrogen atoms of SPC/E model are assigned with charges.

# Charge_Style
coul Ewald 12.0 1E-5
coul Ewald 100.0 1E-5

2 boxes are used as following, one for liquid and one for gas

2
cubic
30

cubic
600.0

The number of water molecules in the box is estimated according to the density of the liquid and gas phases at this temperature.

# Start_Type
make_config 860
make_config 90

I also tried with other different box sizes and water molecule numbers, but I always found that it was very hard to reach the equilibrium. Although the initial density of the liquid and gas phases is set to close to the value of the estimated equilibrium states, the number of water molecules in each box may still undergo significant changes.

Could you please advise me on how to set the initial condition so the simulation can reach equilibrium much faster? Or did I possibly do something wrong with simulation?

Any help would be greatly appreciated!