[gmx-users] [Fwd: some questions about simulate a liquid-vapor interface of a solution, many thanks]

[Mark Abraham]

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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 <parabola1981 at yahoo.com.cn>
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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