Simulations of Mpemba Effect in WATER, Lennard-Jones and Ising Models: Metastability vs Critical Fluctuations

TL;DR

This study uses molecular dynamics simulations to investigate the Mpemba effect in water, Lennard-Jones fluids, and magnetic systems, revealing different underlying mechanisms such as metastability and critical fluctuations.

Contribution

It demonstrates the occurrence of the Mpemba effect across diverse models and identifies distinct mechanisms driving it, including metastability in water and critical fluctuations in Lennard-Jones fluids.

Findings

Mpemba effect observed in water, Lennard-Jones, and magnetic models.

Different mechanisms: metastability in water, critical fluctuations in LJ.

Effect independent of cooling rate.

Abstract

Via molecular dynamics simulations we study ICE formation in the TIP4P/Ice model that is known to describe structure and dynamics in various phases of WATER accurately. For this purpose well equilibrated configurations from different initial temperatures, Ts, belonging to the fluid phase, are quenched to a fixed subzero temperature. Our results on kinetics, for a wide range of Ts, following such quenches, show quicker crystallization of samples that are hotter at the beginning. This implies the presence of the puzzling Mpemba effect (ME). Via a similar study, we also identify ME in fluid to solid transitions in a Lennard-Jones (LJ) model. In the latter case, the ME appears purely as an outcome of the influence of critical fluctuations on the nonequilibrium growth process, for which we present interesting scaling results. For the TIP4P/Ice case, on the other hand, we show that delay in nucleation, due to metastability, can alone be a driving factor for the exhibition of ME. To substantiate the difference between the two cases, we also present LJ-like scaling results for ME in a magnetic transition. Our simulations indicate that in each of the systems the effect can be observed independent of the cooling rate that may vary when samples from different Ts are brought in contact with a heat reservoir working at a fixed lower temperature.