Massively parallel molecular dynamics simulation of formation of ice-crystallite precursors in supercooled water: incipient-nucleation behavior and role of system size.

Abstract

Ice-crystallite precursor formation in supercooled water was studied via molecular dynamics for systems ranging from ∼10^{6} to 8.6×10^{6} molecules, using a tetrahedrally biased single-site "mW" model. This has established system-size effects in the early onset of nucleation, so as to study often-transient precursors' beguiling propensity to "flicker" into instantaneous locally ordered molecular arrangements redolent of ice. In addition, the adoption of solidlike and liquidlike bimodal local configurational-energy distributions was observed, characteristic of early nucleation. Larger systems favored a higher probability of precursor formation, although such ones were not usually longer lived relative to those in smaller systems (which themselves are rather transient). It was concluded tentatively that subtle effects of differences in systemwide density fluctuations and accessible lower-frequency modes tend to favor precursor formation in larger systems, although not necessarily the precursor's kinetic stability.