Finding entanglement points in simulated polymer melts

There are two complementary views of entanglement in polymer melts: a continuous tube confining transverse motions of a given chain and discrete binary entanglement points with neighboring chains. The discrete view is implicit in chain-shrinking studies of simulated entangled melts, while our recent isoconfigurational ensemble (ICE) technique determines a continuous primitive path and confining potential. Here, we reconcile these competing views by identifying points of close contact along the ICE primitive path in an entangled ring polymer melt. We set a minimum distance criterion such that the number of close contacts is equal to the number of entanglement strands, which gives on average about two nearby entanglement points acting on any primitive path segment, a sensible result. We show that both the continuous primitive path and the discrete close contacts are long-lived for ring melts, for which topological confinement effects are expected to be permanent.