[lammps-users] Pair_coeff regarding

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1

Hi Users
I am simulating porphyrin in water
I need a little help with pair_coeff section of the input file

pair_style hybrid lj/charmm/coul/long 8 10 tersoff

pair_coeff * * tersoff SiC.tersoff NULL C # C-C
pair_coeff * * tersoff BCN.tersoff NULL N # N-N

pair_coeff 1 1 lj/charmm/coul/long 0.046 0.4000135 # H-H
pair_coeff 2 2 lj/charmm/coul/long 0.1521 3.150574 # O-O
pair_coeff 3 3 lj/charmm/coul/long # C-C
pair_coeff 4 4 lj/charmm/coul/long # N-N
pair_coeff 1 2 lj/charmm/coul/long 0.0836 1.77529375 # H-O
pair_coeff 1 3 lj/charmm/coul/long 0.0567 1.97503 # H-C
pair_coeff 2 3 lj/charmm/coul/long 0.10318 3.3503 # O-C
pair_coeff 3 4 lj/charmm/coul/long # C-N
pair_coeff 1 4 lj/charmm/coul/long # H-N
pair_coeff 3 4 lj/charmm/coul/long # C-N
pair_coeff 2 4 lj/charmm/coul/long # O-N

Can anyone share the LJ potentials of the above left over pairs of atoms.
I obtained LJ potentials for C, 3.550053 A and 0.07kcal/mol, calculated from a small molecule. I just want to verify it.
Can anyone share the same for N, and from that I believe I can calculate for other pairs.

Also can I use tersoff potential for C-C from SiC or BCN.tersoff? ( question based on a tutorial video)

Thank you

2

Potential parameters are not simply based on elements but have to consider the chemical environment and overall conditions. That casts serious doubts on your existing input (which has obvious syntax errors to boot and makes it impossible to give a meaningful and trustworthy answer. Also you must not just mix and match different pair styles without careful consideration and testing.

Axel.