Temperature-dependent mechanisms of homogeneous crystal nucleation in quenched Lennard-Jones liquids: Molecular dynamics simulations

We have observed homogeneous crystal nucleation in Lennard-Jones liquid by molecular dynamics simulations. A clear nucleation time delay has been observed at $T=0.677T_m$ and $T=0.629T_m$ indicating the presence of a barrier, in contrast to recent reports [Trudu et al., Phys. Rev. Lett. 97, 105701 (2006)]. The structure of nuclei observed in the previous results and in the present work is evidence of transient-time dominated nucleation, not of a spinodal. Very rapid nucleation is observed at $T=0.484T_m$, indicating either a low (but finite) barrier or possibly a spinodal transformation. No spinodal effect has been observed in similar simulations of crystal nucleation in aluminum at any temperature [Aga et al., Phys. Rev. Lett. 96, 245701 (2006)], suggesting that different qualitative behaviors may be possible in what would seem to be similar potentials.

Figure 1

(Color online) (a) Representative trend of clusters vs time at $T=0.677T_m$. Every size of clusters is included. A clear time lag before the rapid growth of clusters is observed in the plot. The onset time is around $153.5\tau$. (b) The size of the largest cluster vs time. Note that the $y$ axis is on a logarithmic scale.

Figure 2

(Color online) Snapshots at $T/T_m=0.677$. Only close-packed atoms are shown in the pictures. The HA method identifies FCC atoms (green or light gray) and HCP atoms (blue or dark gray). We show the arguable diffuse and fractural nuclei at $155\tau$ which become compact and spherical at later stages.

Figure 3

(Color online) Representative trend of clusters vs time at $T=0.484T_m$. The clusters appear essentially instantaneously after quench, which is different from the observations at higher temperatures.

Figure 4

(Color online) Snapshots at $T/T_m=0.484$. Only close-packed atoms are shown in the pictures. The HA method identifies FCC atoms (green or light gray) and HCP atoms (blue or dark gray). The nuclei have no well-defined cores or clearly differentiated surfaces.