Study of Transient Nuclei near Freezing

The molasses tail in dense hard core fluids is investigated by extensive event-driven molecular dynamics simulation through the orientational autocorrelation functions. Near the fluid-solid phase transition, there exist three regimes in the relaxation of the pair orientational autocorrelation function, namely the kinetic, molasses (stretched exponential), and diffusional power decay. The density dependence of both the molasses and diffusional power regimes are evaluated and the latter compares with theoretical predictions in three dimensions. The largest cluster at the freezing density of only a few sphere diameter in size persist for only about 30 picoseconds (~ 2.8 x 10^{-11}[s]). The most striking observation through the bond orientatinal order parameter is the dramatic increase of the cluster size as the freezing density is approached.

💡 Research Summary

This paper presents a comprehensive investigation of the transient structural motifs that appear in dense hard‑sphere fluids as the system approaches the fluid–solid transition. Using large‑scale event‑driven molecular dynamics (EDMD) simulations, the authors followed millions of hard spheres over time spans that reach tens of picoseconds, allowing them to resolve the full temporal evolution of the pair orientational autocorrelation function, C₂(t). Their analysis reveals that the relaxation of C₂(t) can be divided into three distinct regimes.

The first, a kinetic regime, dominates at the shortest times (sub‑picosecond) and is governed by direct binary collisions; C₂(t) decays very rapidly in this window. The second regime, termed the “molasses” regime, exhibits a stretched‑exponential decay of the form exp