efactor 
    <LI>
    class2/cutoff 
    <LI>
    lj/charmm = LJ with charmm switched region that goes smoothly to zero
</UL>
<PRE>
coeffs:  none
               no other parameters required
         lj/cutoff
               (1) cutoff (distance units)
               (2) offset flag (0 or 1)
         lj/smooth
               (1) inner cutoff (distance units)
               (2) outer cutoff (distance units)
         lj/shift
               (1) cutoff (distance units)
               (2) offset flag (0 or 1)
  