goes smoothly to zero 
    <LI>
    ewald = use Ewald summations for long-range effects 
    <LI>
    pppm = use particle-mesh Ewald for long-range effects 
    <LI>
    charmm/switch = use the charmm switch to go smoothly to zero 
    <LI>
    debye = add a Debye/Huckel screening exponential
</UL>
<PRE>
coeffs:  none
               no other parameters required
         cutoff
               (1) cutoff distance (distance units)
         smooth
               (1) inner cutoff (distance units)
               