# defining multiple interaction in lj

Dear Lammps dev

I have a problem defining multiple interaction in lj. I want to define a lj potential between BN sheet and carbon and I already have the parameters between them, but in pair_coeff, the atom type i,j must be defined but now i want the interaction is between BN-C.

B = type 1
C = type 2
N = type 3

sigma = 0.003660
epsilon = 3.390

so by using pair_coeff how should i write it? Like this?

pair_coeff 1 2 lj/cut 0.003660 3.39
pair_coeff 2 3 lj/cut 0.003660 3.39

regards
min

Dear Lammps dev

I have a problem defining multiple interaction in lj. I want to define a lj
potential between BN sheet and carbon and I already have the parameters
between them, but in pair_coeff, the atom type i,j must be defined but now i
want the interaction is between BN-C.

B = type 1
C = type 2
N = type 3

sigma = 0.003660
epsilon = 3.390

so by using pair_coeff how should i write it? Like this?

pair_coeff 1 2 lj/cut 0.003660 3.39
pair_coeff 2 3 lj/cut 0.003660 3.39

well, have you tried it? does it work? does it give a reasonable behavior?

axel.

The results are unreasonable

The results are unreasonable

which begs the question: how do you know it is due to the LJ settings?
and how do you conclude they are unreasonable?

as you hopefully see now, it is near impossible to make any statement
with only a small fragment of information.

axel.

Just a quick observation:

You have 3 types of atoms. There should be 6 (=N*(N+1)/2, N=3)
distinct pairs of atom types. But you only have 2 pair_coeff
commands. This should cause LAMMPS to crash.

I assume there is more to your LAMMPS script that you did not share with us.

I can not tell you what those parameters should be, but I will remind
you that the interactions you did not specify ("pair_coeff 1 3") will
be determined by mixing rules:
http://lammps.sandia.gov/doc/pair_modify.html

If you are having problems, then you should check your other epsilon
and sigma parameters, specifically. "1 1", "2 2", and "3 3":

pair_coeff 1 1 lj/cut ? ?
pair_coeff 2 2 lj/cut ? ?
pair_coeff 3 3 lj/cut ? ?

(or do you have a "Pair Coeffs" section in your data file?)

Cheers

Andrew

I am attempting to assign interaction between BN sheet and graphene, I used tersoff potential to define independent sheet and use lj in between them and I used this command:

pair_style hybrid tersoff lj/cut 3.0
pair_coeff * * tersoff BNC.tersoff B C N
pair_coeff 1 2 lj/cut 0.003660 3.39
pair_coeff 2 3 lj/cut 0.003660 3.39

Dear Lammps dev

I have a problem defining multiple interaction in lj. I want to define a lj
potential between BN sheet and carbon and I already have the parameters
between them, but in pair_coeff, the atom type i,j must be defined but now i
want the interaction is between BN-C.

B = type 1
C = type 2
N = type 3

sigma = 0.003660
epsilon = 3.390

so by using pair_coeff how should i write it? Like this?

pair_coeff 1 2 lj/cut 0.003660 3.39
pair_coeff 2 3 lj/cut 0.003660 3.39

Just a quick observation:

You have 3 types of atoms. There should be 6 (=N*(N+1)/2, N=3)
distinct pairs of atom types. But you only have 2 pair_coeff
commands. This should cause LAMMPS to crash.

I assume there is more to your LAMMPS script that you did not share with us.

I can not tell you what those parameters should be, but I will remind
you that the interactions you did not specify (“pair_coeff 1 3”) will
be determined by mixing rules:
http://lammps.sandia.gov/doc/pair_modify.html

If you are having problems, then you should check your other epsilon
and sigma parameters, specifically. “1 1”, “2 2”, and “3 3”:

pair_coeff 1 1 lj/cut ? ?
pair_coeff 2 2 lj/cut ? ?
pair_coeff 3 3 lj/cut ? ?

(or do you have a “Pair Coeffs” section in your data file?)

Cheers

Andrew