Tersoff Potential Formatting for SiN System

Dear all,
I am currently working on a project to simulate a Silicon Nitride (SiN) system using LAMMPS with Tersoff potentials. I have set up my LAMMPS input script and created a Tersoff potential file for Si and N interactions, based on values from a paper (DOI: Hydrogen role on the properties of amorphous silicon nitride | Journal of Applied Physics | AIP Publishing).
Here is my LAMMPS input script:

# Initialize simulation
units metal
dimension 3
boundary p p p
atom_style full

# Create atoms
lattice diamond 5.43
region box block 0 2 0 2 0 2
create_box 2 box    # Define 2 atom types (Si and N)
create_atoms 1 box   # Create Si atoms in the box
create_atoms 2 box   # Create N atoms in the box

# Define mass for atom types
mass 1 28.09  # Silicon
mass 2 14.01  # Nitrogen

# Define potential
pair_style tersoff
pair_coeff * * SiN.tersoff Si N 

# Perform a calculation
run 100

My Tersoff potential file is as follows:

# Tersoff potential for Si and N
# e1 e2 e3 m   gamma lambda3  c    d   costheta0 n   beta  lambda2 B    R      D    lambda1 A
Si Si Si  1.7322 1 2.4799 100390 1.6217 -0.59825 0.78734 0.0000011 0 471.18 2.7 0.3 2.4799 1830.8
Si Si N   1.7322 1 2.4799 100390 1.6217 -0.59825 0.78734 0.0000011 0 471.18 2.7 0.3 2.4799 1830.8
Si N  Si  1.7322 1 2.4799 100390 1.6217 -0.59825 0.78734 0.0000011 0 471.18 2.7 0.3 2.4799 1830.8
Si N  N   2.7 1 5.43673 20312 2.55103 -0.56239 1.33041 0.0052938 0 511.76 1.8 0.3 5.43673 6368.14
N  Si Si  1.7322 1 2.4799 100390 1.6217 -0.59825 0.78734 0.0000011 0 471.18 2.7 0.3 2.4799 1830.8
N  Si N   1.7322 1 2.4799 100390 1.6217 -0.59825 0.78734 0.0000011 0 471.18 2.7 0.3 2.4799 1830.8
N  N  Si  2.7 1 5.43673 20312 2.55103 -0.56239 1.33041 0.0052938 0 511.76 1.8 0.3 5.43673 6368.14
N  N  N   2.7 1 5.43673 20312 2.55103 -0.56239 1.33041 0.0052938 0 511.76 1.8 0.3 5.43673 6368.14

When I try to run the simulation, LAMMPS gives me an error: “Illegal Tersoff parameter (src/MANYBODY/pair_tersoff.cpp:510)”. I am running LAMMPS-omp 2022-06-23 on a Linux-based high-performance computing (HPC) cluster (the latest version we have).

Looking at my Tersoff potential file, the values for m, gamma, lambda2, and costheta0 parameters are identical for Si-Si, Si-N, and N-N interactions, which I am uncertain about. I could not find these specific parameters in the referenced paper.
Can anyone guide me on how to correctly format Tersoff potential parameters from the literature for use in LAMMPS please?
Thank you!
Brahim

All the info you need is in the documentation for pair style tersoff.

Specifically, there is a statement:

The value of m must be 3 or 1

However in your potential file, that value is either 1.7322 or 2.7 and that is why you are getting the Illegal Tersoff parameter error message.

2 Likes

Thanks a lot for your clarification! I initially mistook ‘m’ for ‘mu’ from the paper’s table. I appreciate your guidance and will read carefully the LAMMPS documentation to better understand the physical significance of ‘m’ (3 or 1) and why it is absent in some publications…

Hi Brahim:
I’m also a beginner of lammps, and I have a question about your potential file. Why the lambda2 is 0? I’m not sure, but I think it should be same as μ in your reference.
image

HELLO, Brahim.
Your silicon nitride tersoff potential function file is ok? I tried to revise it, but it never worked out. Could you please share your potential function file.thank you very much!!!


I don’t know how to set two body parameters and three body parameters from the figure, can someone explain?

You can do it the other way around - find a Tersoff parameter file and its corresponding publication. Then you should be able to reverse-engineer which number in the file is which parameter.