Preference for fcc atom stacking observed during growth of defect‐free LJ₃₂₈₁ clusters

Abstract

Growth simulations of 3-dimensional Lennard-Jones (LJ) clusters/nuclei from the vapor phase were carried out in order to estimate the role of kinetic and energetic effects in determining the internal structure of the clusters. The simulated growth was realized from N = 3281 up to ca. 10000 atoms at two reduced growth temperatures T * = 0.3 and 0.5 and the vapor atom concentration n v = 0.002 (in reduced units of LJ system). During growth at the low temperature, clusters evolve from octahedral to an irregular shape, while at the higher one they become spherical. Statistics of newly created structural units shows a strong preference for the formation of fcc units with their number approximately 3-4 times larger than those of the hcp units. The possible explanation of this preference is by: (1) a larger surface diffusion leading to near spherical shape of clusters, (2) an energetic effect caused by different interaction energy of two fcc or hcp layers located on the neighboring {111} planes, and (3) an entropic effect in the form of disappearance of hcp island on the closepacked fcc layers.

Stable growth of fcc phase achieved in simulations of defected Lennard-Jones clusters

“…However, until N ≈ 6000 they disappeared transforming to a fcc layer. This transformation can be explained by energetic and entropic effects, which prefer the fcc layer stacking instead of the hcp stacking as observed in simulations of the ideal octahedral LJ 3281 [14] in accordance with the results reported by Somasi et al [15]. Only in sufficiently large clusters, the hcp monolayers are able to survive to be covered by the next layer and form a permanent stacking fault.…”

“…At the same growth conditions (T * = 0.50, n v = 0.002/σ 3 ), the ideal octahedral fcc cluster (fig. 1a) grows relatively slowly, as can be concluded from the twenty simulations runs in recent computations [14]. There it was found that on average 88100 ± 1900 MC cycles are necessary to increase the ideal cluster size up to N ≈ 5920.…”

The non-classical nucleation of crystals: microscopic mechanisms and applications to molecular crystals, ice and calcium carbonate

“…The critical nucleus is a small crystalline cluster. Such clusters have been extensively studied [133][134][135][136][137][138] and it is now well established that the 139 showing a computer simulation configuration obtained on attempting to crystallise a system of Lennard-Jones molecules (shown as red spheres), in the presence of impurity molecules (grey spheres) 139 . The impurity molecules have a high affinity for the crystallising molecules and so are incorporated in the growing crystal, but are larger than the crystallising molecules and so strain the growing lattice.…”

“…The critical nucleus is a small crystalline cluster. Such clusters have been extensively studied133 – 138 and it is now well established that the free energy is not minimised by the small crystallite being a defect-free piece of bulk lattice; it is minimised by an often intricate pattern of defects. Two example minima, chosen because of their different defect patterns, are shown in Fig.…”