Error in Lammps script that needs correction

LAMMPS LAMMPS Beginners
1

I am attempting to write a simple lammps script in which I simulate the melting of iron, however when I run the script below, the potential energies of the atoms in my system does not change, telling me that my atoms are not moving at all I have tried many fixes, including changing the integration time, changing which command I use to ramp the temperature, changing the bounds of my simulation box, decreasing and increasing the number of atoms in my system, and more. I am sure that there is something basic I am missing as I am a beginner to this program please help.

Thanks,

Here is my script

Initialize simulation parameters

units metal
dimension 3
boundary p p p
atom_style atomic

Define the simulation box

lattice fcc 3.55
region box block 0 5 0 5 0 5 units lattice
create_box 1 box
create_atoms 1 box

Set the interatomic potential

pair_style eam/alloy
pair_coeff * * Fe_mm.eam.fs Fe

Define the initial temperature

velocity all create 300.0 87287 dist gaussian

Set simulation parameters

timestep 1.0e-12
thermo 100
thermo_style custom step temp pe etotal vol atoms press

Begin equilibration

reset_timestep 0
fix 1 all nve
run 1000
unfix 1

Begin temperature ramp

reset_timestep 0
fix 1 all langevin 1 10000 1e-12 79283
fix 2 all nve
run 10000
unfix 1

Output final configuration

dump 1 all atom 1000 final.dump
run 1

2

Hello,
Since you are using metal unit system, the time is already defined in pico-second (1e-12). Therefore, using a timestep of 1e-12 gives you something in yocto-second (10^-24)…
Simon

3

Hi Simon, Thank you for your response, When I change the integration time to 1 I get a separate error telling me that all of the atoms in my system are lost.

Thanks,

4

If you set the timestep to 1, then it is 1 pico-second with metal units. I don’t know anything about your system, so don’t trust me blindly on this, but I think that 0.001 (i.e. 1 femto-second) would be more appropriate.

5

I tried this fix and the moment that the temperature ramp begins all of the atoms are lost.

6

Oh I am sure there are other problem in the script, like improper parameters in the Langevin thermostat.

7

changing my Langevin thermostat parameters solved my issue Thank you Simon.