Turn off pair-interaction within a specific molecule

Dear all,

I’m currently simulating a system composed of three different types of molecules. For one type of molecule, I intend to turn off LJ interaction between the atoms(beads). But I don’t want to turn off the LJ interaction among the beads for other two types of molecules. There are two questions I encountered. First, is it possible in lammps to exclude all LJ/coul interactions within a molecule. For instance, I want to turn off the pair interactions between the bead 1 and bead 7, which are not directly connected through bonds, angles, or dihedrals. The ‘special bond’ command only excludes LJ interaction at most the first to the fourth bead which are connected through dihedrals. Second, is it possible in lammps that I can exclude LJ interaction within one type of molecule but not in other two types of molecules? I know ‘special bond’ does not do this, because it overwrites if i define it again.


The neigh_modify exclude command has a molecule group option.

Which allows you to turn off interactions if the 2 particles

are in the same molecule and same group. So if you make a group

out of the one type of molecule you want to turn off, it should work.