Analysis of Ice Crystal Growth Shape under High Pressure Using Molecular Dynamics Simulation

A molecular dynamics simulation was conducted to analyze the growth shape of an ice crystal from water near its melting point under high pressure. The simulation was performed using a constant-volume system in which a cylindrical ice crystal grew freely in all directions perpendicular to the crystal’s c -axis. As the ice crystal grew in the system, the pressure gradually increased to approximately 2000 atm. The growth rate gradually decreased to near zero because the increase in pressure caused melting point depression. As the pressure increased to 2000 atm, the ice crystal grew as a hexagonal plate with {101̅0} prismatic plane facets clearly visible. The simulation indicated a fluctuation of the growth front geometry in the a -axis direction; the formation of a molecularly sharp corner was repeatedly disrupted during growth. The molecularly sharp corner appeared transiently as a result of the layer-by-layer growth of prismatic plane layers toward the corner. When corner formation was disrupted, a transient, molecularly flat, {112̅0} secondary prismatic plane appeared, but it was not a stable plane facet. The features of the ice crystal growth shape observed in this simulation were then compared with real systems.