How to reach the information of other atoms in a molecule in lammps

Thank you for your reply.

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So, my molecules are small (3-5 atoms). Can you point out an example of
building "molecule" neighbor list?

i don't think there is yet an *exact* match for what you are looking
for but something similar. but the airebo pair style compiles a list
of so-called "REBO neighbors" in the REBO_neigh() function, similarly
comb, bop and others have a list of "near" neighbors. what i am
suggesting is that you adapt this to rather then selecting by
distance, you would select by molecule id.