Scalar activity induced phase separation and liquid–solid transition in a Lennard-Jones system

Molecular dynamics simulations are used to investigate the effects of scalar activity in a three-dimensional system of Lennard-Jones particles at state points spanning from the gas to the liquid regime. Scalar activity is introduced by increasing the temperature of half of the particles (labeled 'hot') while keeping the temperature of the other half (labeled 'cold') constant at a low value. The ratio of the temperatures of the two subsystems is considered to be a measure of scalar activity. We observe that the two species tend to phase separate at sufficiently high temperature ratio. The degree of phase separation is quantified by a suitably defined order parameter and the entropy production in the process of phase separation is determined by employing the two-phase thermodynamics (2PT) method. We observe that the degree of phase separation and the entropy production increase with the density of the system. The mean number of clusters and the mean size of the largest cluster are determined as functions of the density and the temperature ratio. A calculation of bond orientation order parameters reveals that the largest cluster develops solid-like order consisting of both FCC and HCP packings.