Wang-Landau Study of a Square-Well Polymer Chain

A homopolymer chain consisting of monomers interacting via a Square Well (SW) potential exhibits a freezing transition from expanded coil to compact crystalline conformations or transitions from coil conformations to collapsed globules and then to crystalline structures. Following the work of Taylor et al.[J. Chem. Phys. 131, 114907 (2009)] we study a homopolymer SW chain of length 156 N = monomers for two different diameters 1.04 λσ = and 1.12 λσ = of the SW potential. For 1.04 λσ = the chain undergoes a discontinuous globule-crystal (freezing) transition. Yet, the collapse (coil-globule) transition is preempted by the freezing transition and thus there is a direct first-order coil-crystal phase transition. For 1.12 λσ = , the system undergoes a collapse transition followed by the freezing transition. Our analysis is based on the accurate determination of the microcanonical entropy of our system obtained by Wang-Landau sampling and transitions are characterised and identified by analysis of our results in the microcanonical and canonical ensembles. Our results are in line with the predictions of Taylor et al.