Tersoff potential for amorphous SiCN and whether residual pressure after NVT melt-quench should be used as a validation criterion

LAMMPS
1

Dear LAMMPS / molecular simulation community,

I am trying to build an H-free amorphous SiCN model for later plasma-surface reaction simulations. The target system is amorphous SiCN with Si:C:N = 1:1:1, using LAMMPS.

My workflow is:

  1. Use a Tersoff potential to generate the amorphous SiCN bulk by melt-quench.
  2. Later cut a slab and switch to ReaxFF for surface chemistry simulations.

The difficulty is the Tersoff potential for SiCN.

From the literature, I found that some SiCN studies mention combining SiC and Si3N4 Tersoff parameters and disabling the N-N attractive interaction. However, I have not found a complete, directly usable LAMMPS Si-C-N Tersoff file with all 27 triplet entries clearly provided.

I therefore have two questions:

  1. Is there a publicly available and well-validated LAMMPS-ready Tersoff potential file for Si-C-N / SiCN?

    • If yes, could someone point me to the original source?
    • If not, what is the recommended way to construct or validate such a combined SiC + SiN Tersoff file?

  2. For amorphous SiCN generated by fixed-volume NVT melt-quench, should the final residual pressure be used as a model-validation criterion?

    In my tests, the simulations can finish numerically without lost atoms, NaN, or warnings, and the RDF / short-bond checks look reasonable. However, the final fixed-volume NVT pressure can remain very large, on the order of -7 to -12 GPa.

    I understand that many amorphous-structure papers mainly validate the model using RDF/PDF, structure factor, coordination statistics, bond-angle distributions, density, and sometimes elastic properties. They do not always report final residual pressure after NVT melt-quench.

    My question is: for a bulk amorphous precursor model that will later be cut into a slab and used for surface reaction simulations, is such a large residual pressure a serious problem? Should I perform an NPT density diagnostic and use the zero-pressure density preferred by the potential, or is it acceptable to use the fixed-density NVT-quenched structure if the local structure metrics are reasonable?

Some details of my current tests:

  • Composition: Si:C:N = 1:1:1
  • Box size: 100 Å × 100 Å × 50 Å
  • Density tested: about 2.40–2.60 g/cm3
  • Timestep for Tersoff: 0.5 fs
  • Melt-quench schedule:
    • minimize
    • 0.1 K NVT 20 ps
    • 0.1 K → 8000 K NVT 20 ps
    • 8000 K → 3000 K NVT 40 ps
    • 3000 K NVT 200 ps
    • 3000 K → 300 K NVT 1000 ps
    • 300 K NVT 10 ps
  • Numerical stability:
    • no lost atoms
    • no NaN
    • no dangerous builds
    • final data/restart files written successfully
  • But final NVT pressure can be around -10 GPa.

Any advice on the correct interpretation of the residual pressure and on reliable SiCN Tersoff parameter sources would be greatly appreciated.

Best regards,