Calculation stopped in lammps

I am trying to simulate adsorption of benzene derivative on copper surface. It was supposed to run for some 2000000 steps but the lammps stopped printing it after some 62100 steps. What could be the problem? No error is there, just only the next values are not printing and it has stuck at 62100. Potential is reaxff , timestep is 0.1 fs and dumping time is 250 fs. Output is displayed at 100fs.

Without knowing more about your system and your LAMMPS version, it is difficult to make any suggestions.

The most common cause for the behavior you describe is that you had some atoms in close contact and thus very high forces which in turn will turn those atoms into fast moving projectiles and then LAMMPS gets “stuck” trying to wrap them back into the principal simulation cell. ReaxFF is particularly sensitive due to its complex potential functions and the use of charge equilibration. So any “bad” geometry situation is often emphasized.

It can help to visualize the trajectory as far as you have it an look out for any unexpected structures or behavior.

It would also be helpful to see the thermodynamic output for the steps leading up to the stalled output. Often the potential or kinetic energy will show anomalies.

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Hi when trying to simulate the complex aromatic molecule, the geometry do gets distorted and calculation stops just as you said. How do I maintain the geometry of the molecule to be adsorbed . Would I be required to use fix restrain so that the dihedrals and angles of molecule are maintained. I just want that my molecule structure doesn’t gets disfigured that need to be adsorbed on the surface under reaxff potential.

When a simulation does not result in the expected geometry then usually there is something wrong. Trying to suppress that unwanted geometry is not the solution. You have to understand why this happens. Possible reasons:

  • you have bad simulations settings
  • you have force field parameters that are unsuitable for that kind of system
  • you have constructed a model (e.g. via pair style hybrid) that is unsuitable in general
  • you have provided incorrect/invalid topology/geometry data
  • you have incorrect expectations of what is the correct geometry