[gmx-users] Re:the vapor-liquid interface of a solution at low pressure

beibei parabola1981 at yahoo.com.cn
Sat Jun 14 02:28:55 CEST 2008

Hi, all
  In fact, I want to verify the hygroscopic of lithium bromide solution, so I want to make some water moleculars in the vapor region. But I found that at 0.008bar, 303K and very small box(the unit of the length of the box is nm), there may be zero vapor moleculars. Thus I think I cannot simulate in this pressure or this temperature.  Can you give me some advice on this topic? thank you very much.

Hi, beibei

The first point made by Mark is to check whether volume stabilizes when
the system is subjected to NPT simulation.

Yang Ye

Mark Abraham wrote:
> Please leave GROMACS-related correspondence on the GROMACS mailing list.
> That way others can follow and contribute to the discussion, and it is
> archived for people to search later.
> Mark
> -------- Original Message --------
> Subject: some questions about simulate a liquid-vapor interface of a
> solution, many thanks
> Date: Thu, 12 Jun 2008 22:40:05 +0800 (CST)
> From: beibei 

> To: mark.abraham at anu.edu.au
> Hi, Mark
> Thank you very much to your reply. I cannot undersand some points in
> your reply. How to compute the volume that will lead to this pressure
> when the system is equilibrated? in addition, do you mean the sysytem is
> sandwich box or the cubic box?
> looking forward to your advice. Thank you very much.
> Best wishes.
> Beibei
> 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.

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