[lammps-users] Why do the potential energy and pressure always oscillate so much?

Dear Steve and Lammps users,

I am simulating a Au nanowire build from bulk lattice constants.
I want to relax the system to its equilibrium.
The pressure a long the transverse direction is ok.
However, the pressure in the length direction and the potential energy of the system oscillate a lot
and do not seem to converge to a stable value, as shown in the attachment.
The following is the main code I have used.

boundary s s s
dimension 3
units metal

lattice fcc 4.08
region 1 block -90 90 -5 5 -5 5
create_box 1 1
create_atoms 1 box

timestep 0.004
fix NVT all nvt 2.0 2.0 0.1 drag 0.2

run 25000

Thank you very much for attention and kind help.



Pressures oscillate. It's the nature of MD. If you
start with free surfaces that are unrelaxed, and let
them go, you may well get oscillations. It's like
releasing a stretched spring and there's nothing
to damp the motion.


Dear Steve,

Thank you.
Is there any possible approach to get rid of the oscillation?
Moreover, if the nanowire is loaded with a external force in the tranverse
directions,it will also oscillate.
It is quite difficult if I want to average the potential energy and the

thanks a lot for attention.


Again, this is more of a MD issue, than a LAMMPS issue.
You can run a bigger system. You can pre-equilibrate free
surfaces with a minimize command, to reduce oscillations
during dynamics. You can damp the motion a few times,
then you should be able to run NVE w/out big osciallations.
But if you are driving the system with a boundary condition
then all bets are off.