I want to prevent a wall from moving

Dear All users

I have a confined system,( normal decanes between two walls of gold). I want to do this:

The bottom lower plane of atoms is prevented from moving in the Y-direction.

How can I do this?


Probably a fix planeforce command is all you need.

fix hold boundary planeforce 0.0 1.0 0.0


2013/2/27 Ali Alizadeh <[email protected]…24…>

I read your email too quickly, and realize you only wanted to prevent
movement in the Y direction. So what I am about to post is probably
irrelevant. If so, then please ignore this post.

Dear Andrew

Thank you very much for your reply,

Using NPT simulations what for? If your system hasn't changed, i.e.,
decane trapped between the gold walls, what are you trying to achieve
with NPT simulations? I have the feeling that what you think you want
is not what you really want.

Dear Carlos

Thank you for your reply,

In fact, I am reproducing the results of a paper, you can see that in this link:


In this paper, in x and z direction there are pbc and in y direction non-pbc,

I see. Your Y dimension there is non-periodic so looks to me all you
have to do is couple the barostat to the x and z dimensions and leave
the y dimension out. See the manual for how to do this.

It is not clear to me what they did from the description of the paper. If the X and Z directions of the cell are changing, does that mean that the density of the solid slabs is changing as well? What is the “thermodynamic equilibration portion of the simulation”?

I only looked quickly at the paper to understand Ali's Q about using
NPT. Could not comment further on the paper details. One could indeed
have changes in density but with a big enough system size they could
be made negligible. Again, did not aim at fully processing that paper
as doesn't interest me.