I am attempting to reproduce a GROMOS force field that contains VDW terms given in the form (A/r**12) - (B/r**6). One atom type has B=0, giving a repulsive VDW term only. CHARMM has the form e(ij) [ (Rmin/r)**12 - 2(Rmin/r)**6 ], so usually it is not a problem to convert the A and B into epsilon(i,j) and Rmin, but how can I reproduce the term where B=0?

Thanks,
James Matthews