Relationship between the liquid–liquid phase transition and dynamic behaviour in theJagla model

Abstract

Using molecular dynamics simulations, we study a spherically symmetric ‘two-scale’ Jaglapotential with both repulsive and attractive ramps. This potential displays a liquid–liquidphase transition with a positively sloped coexistence line ending at a critical pointwell above the equilibrium melting line. We study the dynamic behaviour in thevicinity of this liquid–liquid critical point. Below the critical point, we find thatthe dynamics in the more ordered high density liquid (HDL) are much slowerthen the dynamics in the less ordered low density liquid (LDL). Moreover, thebehaviour of the diffusion constant and relaxation time in the HDL phase followsapproximately an Arrhenius law, while in the LDL phase the slope of the Arrhenius fitincreases upon cooling. Above the critical pressure, as we cool the system at constantpressure, the behaviour of the dynamics smoothly changes with temperature.It resembles the behaviour of the LDL at high temperatures and resembles thebehaviour of the HDL at low temperatures. This dynamic crossover happens in thevicinity of the Widom line (the extension of the coexistence line into the one-phaseregion) which also has a positive slope. Our work suggests a possible generalrelation between a liquid–liquid phase transition and the change in dynamics.