Fig. 3: Microscopic ordering pathway at dendrite tip and zigzag edge.

a–c, f–h Structural evolution of the dendrite tip growth from a 65- to 66-type structure (a–c) and the zigzag edge growth from a 665- to 666-type structure (f–h). a, f demonstrate one typical trajectory of the time-lapse molecular dynamics (MD) snapshots during the growth from bilayer pentagonal defect to hexagonal crystal structures. b, c and g, h present the spatial distribution of the top (b, g) and bottom (c, h) layer molecules sampled along the 65 to 66 and 665 to 666 ordering paths (fenced in white boxes in d, i). The molecules are colored according their perpendicular height z above the substrate. The incorporation of the 6-th molecules into the 5-membered rings are circled and pointed by green and red arrows in the top and bottom layers. d, i Clustering of MD local configurations at dendrite tip (d) and zigzag edge (j) on the plane of two principal components PC1 and PC2 encoded by the machine learning algorithm. The color denotes the number counts of each local structure. The trajectories displayed in a, f are highlighted by the magenta pathways. e, j The potential energy per molecule ∆E as function of PC1. Both values are averaged over the growth front water molecules highlighted in orange as inset configurations. The zero energy baselines are set to be the potential energy of the 65- and 665-type structures.