         fene/standard
               (1) k for FENE portion (energy/distance^2 units)
               (2) r0 for FENE portion (distance units)
               (3) epsilon for LJ portion (energy units)
               (4) sigma for LJ portion (distance units)
          fene/shift
               (1) k for FENE (energy/distance^2 units)
               (2) r0 for FENE after shift is performed (distance units)
               (3) epsilon for LJ (energy units)
               (4) sigma for LJ after shift is performed