The phase diagram and melting scenarios of two-dimensional Hertzian spheres

Abstract

ABSTRACTWe present computer simulations of a system of purely repulsive soft colloidal particles interacting via the Hertz potential and constrained to a two-dimensional plane. This potential describes the elastic interaction of weakly deformable bodies and can be a reliable model for a qualitative description of behaviour of soft macromolecules, such as globular micelles and star polymers. We have found a large number of ordered phases, including dodecagonal quasicrystal, and analysed the melting scenarios of low-density triangle and square phases. It is interesting that depending on the position on the phase diagram, the system can melt both through the first-order transition and in accordance with the Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young scenario (two continuous transitions with an intermediate hexatic phase) as well as according to recently proposed two-stage melting with the first-order hexatic–isotropic liquid transition and continuous solid–hexatic transition. We have also demonstrated the possibility of a tricritical point on the melting line and have found the line of a water-like density anomaly on the phase diagram.