[lammps-users] using fix box/relax command

Dear Lammps users
I’m running a tensile test on CNT-Al nanocomposite
For the energy minimization I’m using the following steps

First Equilibrium step -----> Conjugate gradient energy minimization algorithm

reset_timestep 0
min_style cg
minimize 1e-6 1 500000 1000000

Second Equilibrium step -----> heat the unit cell from 0 to 700 K then anneal it to 300 K

timestep 1e-5
fix 1 all temp/rescale 1 0 700 0.02 0.5
fix 2 all nve
run 1000000
unfix 1
unfix 2
reset_timestep 0
timestep 1e-5
fix 1 all temp/rescale 1 700 300 0.02 0.5
fix 2 all nve
run 1000000
unfix 1
unfix 2

Third Equilibrium step -----> relax the structure at constant pressure of 0 bar and constant temperature of 300 K

reset_timestep 0
timestep 1e-3
fix 1 all npt temp 300 300 (100.0*dt) aniso 0 0 (1000.0*dt)
run 100000
unfix 1

I want to use the command fix box/relax to further relax the atoms and expand the simulation box a little, my questions are
Shall I use this command as a fourth step, or I need to use along one of the three steps?
and shall I use an iso keyword with zero pressure or negative pressure?

Thank you and regards

Isra

Fix box/relax is only used by minimization, not by dynamics. You can try it.
Or you could just use the change_box command to expand the box and dilate
the atoms, then run some more dynamics. Or use fix deform with dynamics
to do it more gradually.

Steve