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Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space
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Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space

From: "罗爽" <luoshuang@...7337...>
Date: Fri, 13 Apr 2018 20:40:25 +0800

Dear Giacomo,
Thanks for your apply 
Pls see the attached PNG file.  In my system, one face of the water system is exposed to the vacuum, the other side is exposed to a rigid surface.   A periodic boundary condition is used at  three directions.  The dimension of the simulation cell in the direction perpendicular to the surface is suffcientlly large to avoid unnecessary interactions due to the PBC.


---------- Origin message ----------
>From:"Giacomo Fiorin" <giacomo.fiorin@...24...>
>To:"罗爽" <luoshuang@...7337...>
>Subject:Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space
>Date:2018-04-13 19:49:02
If I understand correctly, you are modeling an air/water interface, where
one face of the water film is exposed to the vacuum. The water film will
inevitably deform to minimize its total surface energy.

If that's not the correct interpretation, can you explain more clearly what
you're trying to model?


On Fri, Apr 13, 2018 at 1:22 AM, 罗爽 <luoshuang@...7337...> wrote:

> Dear Lammps users
> The simulation system contains a rigid surface and a water film of 5-7
> layers molecules sitting on the surface. To avoid unnecessary
> water-surface interactions caused by PBCs, a void space above the water is
> used. I am looking a way to model the Couette flow of water in this
> system. I know that the linear velocity profile of the fluid can be
> obtained by dragging a wall or used fix nvt/slood and fix deform commands.
> But I don't want my box be deformed and I also don't want the water
> confined in a channel. I tried to add a velocity paralleling to the
> surface to water molecules in the upper-most layers. However, the volume
> of the water is changed due to the void space. Thus, it's difficult to
> define the water molecules in the upper most layer. How can I do to get
> the couette flow in this system?
> Any help will be highly appreciated
> Thank you all very much
> Luo
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Giacomo Fiorin
Associate Professor of Research, Temple University, Philadelphia, PA
Contractor, National Institutes of Health, Bethesda, MD