Buckingham potential for polymers

[Vemparala Satyavani <vani-: at :-baton.phys.lsu.edu>]

 The Buckingham potential has the form Aexp(-rB)-c/r^6. isn't it true
 that with this potential, when particle come closer than a distance,
 there is actually a huge attractive well? what actually prevents the
 particels to come closer? The repulsion part(aexp(-rB)) cannot actually
 counteract the attractive part at small distances. Combined with
 Coulomb(the attractive part), iam having some pathological conditions in
 the system.
 And also what is the best way to get an initial configuration? now iam
 just placing the chains on some lattice in a bigger box( so that they are
 well seperated) and then performing Pivot Monte Carlo on them before i
 Actually do MD. Is there a better way to get initial state? I suspect the
 initial state may be a problem for me.
 and finally even if i start at such a state, where the chains are well
 seperated, when MD is performed, there is a huge probability that any of
 the nonbonded atoms might come closer, and iam having similar problems
 irrespective of the size of the box.
 what is the best way to avoid the huge attractive well in the potential?
 Thanks a lot
 Vani