Cluster Structure of Collapsing Polymers

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In order to better understand the geometry of the polymer collapse transition, we study the distribution of geometric clusters made up of the nearest neighbor interactions of an interacting self-avoiding walk. We argue for this new correlated percolation problem that in two dimensions, and possibly also in three dimensions, a percolation transition takes place at a temperature lower than the collapse transition. Hence this novel transition should be governed by exponents unrelated to the θ-point exponents. This also implies that there is a temperature range in which the polymer has collapsed, but has no long-range cluster structure. We use Monte Carlo to study the distribution of clusters on the simple cubic and Manhattan lattices. On the Manhattan lattice, where the data are most convincing, we find that the percolation transition occurs at ωp=1.461(3), while the collapse transition is known to occur exactly at ωθ=1.414…. We propose a finite-size scaling form for the cluster distribution and estimate several of the critical exponents. Regardless of the value of ωp, this percolation problem sheds new light on polymer collapse.

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