Fig. 4.

Homogeneous nucleation simulations of ice performed using ML-BOP_dih. System dynamics and evolution of structural motifs during the cooling phase from homogeneous nucleation leading up to the grain boundary formation and grain growth (Supplementary Movie 1). a The total potential energy variation of the 2 million-water molecule system during the cooling phase from 275 to 210.5 K and at longer times when the system temperature is kept constant at 210.5 K. We identify four distinct stages: an initial quiescent time shown by the red line when no nucleation event occurs; the nucleation followed by an initial slow transformation shown by the slow energy decreasing period in green; a fast transformation phase of the grains shown by the rapid decrease in potential energy in blue; and a plateauing of potential energy shown in purple marks the completion of the phase transformation. b The snapshots show the subcritical water nuclei during the long quiescent phase leading up to the nucleation. The first nucleation event for the 2 million-water system occurs at t = 130 ns. Liquid water molecules are not shown for clarity. c MD simulation snapshots showing the various stages of grain growth and grain boundary during the post-nucleation stage. Blue, brown and green spheres represent cubic, hexagonal and amorphous ice, respectively. Liquid water is omitted for clarity. d The temporal evolution of the number of subcritical water nuclei (size <100 molecules) from the quiescent period and the initial appearance of stable nuclei during the post-nucleation stage. e The corresponding temporal evolution of the fraction of cubic and hexagonal ice