Non-numeric pressure - simulation unstable

LAMMPS LAMMPS Beginners
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1

Hello all
I have made a random solid alloy in my LAMMPS script using a pre-existing potential file and need to equilibriate the system using an NPT ensemble, but I keep getting the error: “Non-numeric pressure -simulation unstable” all the time, each time with a different error code. My structure and the relaxation process are as follows:

units metal
boundary p p p
atom_style atomic

lattice fcc 4.64

region 5 block 0 32.49 0 32.49 0 32.49
create_box 5 5
create_atoms 1 box
create_atoms 2 box
create_atoms 3 box
create_atoms 4 box
create_atoms 5 box

set region 5 type/ratio 1 0.40 12345
set region 5 type/ratio 2 0.30 67890
set region 5 type/ratio 3 0.20 24680
set region 5 type/ratio 4 0.05 13579
set region 5 type/ratio 5 0.05 45678

pair_style eam/alloy
pair_coeff * * FeNiCrCoCu-heafixed.setfl Fe Ni Cr Co Cu

reset_timestep 0
timestep 0.001
fix 5 all npt temp 300.0 300.0 0.5 iso 0.0 0.0 10.0 drag 1.0

thermo_style custom time step temp ke pe press etotal
thermo 100

run 10000

Also, when I try to minimize the energy, it runs the first step and shows NaN for pressure and energies and won’t continue anymore.

thanks for your help in advance,
Ali

2

Where did you get this piece of input from?
You are creating 5 types of atoms directly on top of each other… No wonder your simulation crashes.

3

This piece of code is also not likely doing what you expect. There have been repeated discussions of how to build systems with different ratios of atom types. The problem here is that the ratio is applied to all atoms, so that the number of atoms of types you set first will be lower than initially set.

4

Thx dear Axel,

I changed my script and used atom_modify together with region and set 5 types and it worked. It made an FCC lattice but I’m not sure how reliable it is.

5

This makes no sense at all. The only atom_modify option that uses regions is the “first” option and that has absolutely nothing to do with your bad choices for commands in your input.

It will create whatever lattice or geometry that you tell LAMMPS to create.

Well, that is essentially your job and part of any any simulation study. For example, have you checked what percentages of the individual atom types you have now? Does it match your expectations?