ilon (energy units)
               (2) sigma (distance units)
               (3) cutoff (distance units)
        lj/smooth
               (1) epsilon (energy units)
               (2) sigma (distance units)
               (3) inner cutoff (distance units)
               (4) outer cutoff (distance units)
        lj/shift
               (1) epsilon (energy units)
               (2) sigma (distance units)
               (3) delta shift distance (distance units)
               (4) cutoff (distance units)
      