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

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#1

Hi,

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.

Regards,
Prerana Rathore

#2

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.

Steve