Exclude the coulombic interaction within a molecule but not L-J


I am simulating stearin (triglyceride of stearic acid) molecules which have some charged particles. I am using pair_style lj/long/coul/long.

I don’t want electrostatic interactions between pair of atoms, if they belong to the same molecule. However, electrostatic interaction between two atoms from different molecules, is allowed.

If, I exclude these interaction with neigh_modify command, then it will exclude L-J interaction also.
If, I assign every atom zero charge, then it will affect my inter-molecular electrostatic interactions.
This is large system, so pair_style hybrid may not help.

Additional information:

These charged groups are making 1-2, 1-3, 1-4, 1-5,1-6 and 1-7 atom pairs. The interaction between 1-2, 1-3 and 1-4 is already excluded by special_bonds command. Now I want to exclude 1-5, 1-6 and 1-7 coulombic interactions.

Can you please tell me if, there is any command, which can do this.

Prerana Rathore

There is no option in LAMMPS that will turn off only part of the pair style

interactions for a pair of atoms in the same molecule. It would have to

be added, e.g. as an option for pair_style hybrid where you could apply

certain neighbor list restrictions to one of the sub-styles.

There is also no physical mechanism I know of that would “turn off”

Coulombic interactions between a pair of charged atoms at opposite ends

of a large molecule.