Thank you for your reply. I am a little confused. If the compute variable command ignores the group, the result of LJ_pair should include all pair LJ interaction in the whole system (not only two particles in my group 1). That is the result LAMMPS gave me before. If I want to get the LJ interaction between only one pair of particle, what can I do?
After I upgrate my LAMMPS to Nov16, 2007 version. my two files pairPotential and attributesFile are still empty. Could you please tell me what is you version?
All the best!