Hi dear LAMMPS users,

In my simulation model, I have 9 kinds of atoms. But I only consider 3

kinds of atoms (A B and C) for simplicity here. My pair_style is

lj/cut/coul/long. The unusual aspects of my model are as follows:

1.For atom pair AA AB AC and BB BC, the lj cutoff distance is R1

2.and for atom pair CC, the lj cutoff distance is R2.

3.And the global coul cutoff is 12A, the lennard-jones parameter can

be computed through pair_modify command, but the cutoff cannot.

To achieve this, I was wondering which method can achieve what I want?

And my input script are as follows, and I have three questions

following each “#”, really appreciate for your kindly help:

Method1:

Read_data atoms.data

Pari_style lj/cut/coul/long R1 12

Pair_modify mix geometric

#question1: Now the LJ parameters for AA AB AC BB BC CC are correct

and the cutoff distance for AA AB AC BB BC is correct(equals R1 here),

but the cutoff distance for atom pair CC is not correct(equals R1 here

but the correct cutoff is R2). So next step I will set it explicitly.

I was wondering whether the pair_modify mix command will take into

account the new pair_coeff for atom CC which I set explicitly on the

next step. So the cutoff for AC and BC is (R1+R2)/2.

Pari_coeff 3 3 0.21 2.96 R2

#question2: Because I want to set the cutoff distance for AC and BC to

R1 explicitly(don’t through pair_modify mix…). So I set pair_coeff for

CC after mix done. I was wondering whether the order between

pair_coeff and pair_modify will influence the results.

Method2:

Read_data atoms.data

Pair_style lj/cut/coul/long R1 12

Pair_coeff 1 3 0.56 3.4 R1

Pair_coeff 2 3 0.53 3.5 R1

Pari_coeff 3 3 0.21 2.96 R2

Pair_modify mix geometric

#question3: I think this method can achieve what I want, cause I set

AC BC CC explicitly and use mix geometric to compute other lj

parameter (AB) which I haven’t set. But when there are many kinds of

atoms, I need to compute and set every lj parameter explicitly. So it

maybe tedious in my simulation. So I was wondering whether method1 can

get the same result as method2 or is there some alternative method.

Thanks for your advisement

Looking forward to your reply.

Sincerely,

Shusen Guo