[gmx-users] how to simulate liquid-vapor interface of a solution at a low pressure

[Mark Abraham]

beibei wrote:
> Hi all, 
>        I want to simulate the liquid-vapor interface of I lithium 
> bromide solution at 303K and 0.008bar. First I put the solution to a 
> cubic box and used NPT ensemble to simulate. Then, I enlarged the box to 
> form two liquid-vapor interface,and used NVT ensemble, but the pressure 
> is not 0.008 bar.

You need to determine a volume that will lead to this pressure when the
system is equilibrated. Then you need to measure for long enough to get
a meaningful average pressure. Trial and error might be the most
effective approach. Best of luck!

> If I used NPT emsemble in the second step, the box 
> becomes smaller with the run time.

Of course... you won't get phase separation at equilibrium in NPT unless
you happen to be at a critical point. Think about heating and cooling a
  closed and open beaker of real water.

>  I want to know how to do when  I 
> want to simulate the liquid-vapor interface of a solution at a low pressure.

Mark