[lammps-users] addforce command

Hi everyone,

I have a question about using addforce command.
In the simulation, a constant load is applied to the bottoms surface of a simulation box. The load is in z direction, so I apply Fx = 0, Fy =0, and Fz = a constant load. But when I analyzed the stress from “compute stress/atom” command, I found out the stress in xx, yy and zz direction have similar non-zero value. I’m confused, as I didn’t apply any load in x and y direction.

Could you please help look at this problem? Thank you very much!


You are adding a force, not setting a force (see fix setforce). So
if the atoms in the surf already have x,y forces they won't be changed.
So stress can persist.