  soft
               (1) prefactor A at start of run (energy units)
               (2) prefactor A at end of run (energy units)
               (3) cutoff (distance units)
        class2/cutoff
               (1) epsilon (energy units)
               (2) sigma (distance units)
               (3) cutoff (distance units)
        lj/charmm
               (1) epsilon (energy units)
               (2) sigma (distance units)
               (3) epsilon for 1-4 interactions (energy units)
               (4) sigma f