Snapshots of the crystallization of water at 180 K, starting from instantaneously quenched liquid (QL). The simulation cell has side. Through panels (a)–(h), the water molecules that belong to the ice cores are shown in blue and all other molecules are hidden. During stage I [panels (a)–(e)], there is an increase in the number and size of the ice nuclei. Stage II starts when the number of ice nuclei peaks at 100 ns [panel (e)] and continues until only a few nuclei result from the process of growth and consolidation. Stage III starts at 300 ns [panel (g)] and involves slow growth and consolidation of the crystallites. At [panel (i)], 80% of the water has crystallized: 50% forms the core of the crystallites (blue), 30% is interfacial ice surrounding them (orange), and 20% remains in the amorphous state between crystallites (green). By , the crystallites had reached sizes of several nanometers and further consolidation is no longer possible through rearrangement in the time scales accessible to the simulations.
(a) Fraction of total, core, and interfacial ice over the course of the 590 ns simulations at 180 K. Orange lines: crystallization of warmed-up LDA glass, WG. Black lines: average for the crystallization of the five instantaneously quenched liquid, QLs. The dashed green lines are the fractions of core ice described by Eq. (4) with the coefficients of Table I. (b) Time evolution of the number of ice nuclei containing ten or more molecules of core ice. The volume of the simulation cell is . Black and orange dots represent the data for the QL and WG simulations, respectively. The lines are running averages to assist the visualization. The dashed vertical lines distinguish three stages in ice crystallization: development of nuclei in stage I, consolidation of neighboring nuclei in stage II, and growth and aging of crystallites in stage III.
Mean square displacement of water at 180 K. The initial mobility is higher for the instantaneously quenched liquid (QL) (black line) than for the warmed glass WG (orange line). The dashed lines show the best fit to Eq. (5). Water mobility in the QL and WG systems is strongly subdiffusive due to the formation of ice crystallites along the simulations. The exponent in Eq. (5) is 0.4 for QL and 0.52 for WG.
Water-water rdf as ice crystallizes from supercooled water at 180 K. The labels indicate the fraction of core ice and the corresponding snapshot in Fig. 1. The curves are displaced vertically to facilitate the visualization. The rdf for 2% ice is duplicated (solid and dashed blue lines) to show how insensitive the rdf is to the changes that occur due to crystallization during stage I. The ice signatures become evident when the system enters stage II and the ice crystallites thicken.
Final structures of water in the six simulation cells after 590 ns at 180 K. The core of the ice crystallites is shown in blue, the interfacial ice in orange, and the liquid between crystallites in green. The WG system has the largest crystallites. The simulation cells are 10 nm per side and periodic in the three dimensions.
Kinetic coefficients that best represent the evolution of core ice in the simulations, according to Eq. (4).
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