How can I exert stress boundary correctly?

Hello, all

I am a new user to lammps.
After read the manual, I have learned there are several ways to
exert boundary condition. Now I want to simulate a box
and exert stress boundary on some faces (because of some reasons,
I think prescribed displacement on these faces isn't appropriate.).

I plan to add a force on each atom of the top three layers of each face
by the command "fix addforce". The force exerted on each atom is
obtained by dividing the total force I want to exert to this face by
the amount of atom of the top three layers.

But I'm not sure is it a correct way to exert boundary condition?
Could anyone give me some advice about it?

Thank you in advance!

Wang Kai

You can use fix addforce on some subset of atoms. Or fix
move to move them in a prescribed fashion. Or you can
use fix deform to stretch the box itself, for example.

Steve

Dear Steve,

Thank you very much for your help!

Actually, what I want to know is if I can calculate
the total force by multiplying the force exerted on
each atom and the amount of atoms?

For example, I exert a "fix addforce 0.1 0.0 0.0" on each
atom of the top three layers of a face, and the amount of
atoms is 662. Then, can I speak I exert a x-axis force
0.1*662=66.2 on this face? Is it a appropriate way to exert
boundary condition? (For some reasons, prescribed displacement
isn't suit for my case.)

Wang Kai

yes, you can sum the force across atoms.

Steve