Ice nucleation by electric surface fields of varying range and geometry

Molecular dynamics simulations are employed to show that electric field bands acting only over a portion of a surface can function as effective ice nuclei. Field bands of different geometry (rectangular, triangular, and semicircular cross sectional areas are considered) all nucleate ice, provided that the band is sufficiently large. Rectangular bands are very efficient if the width and thickness are ≳0.35 nm, and ≳0.15 nm, respectively, and the necessary dimensions are comparable for other geometries. From these simulations we also learn more about the ice nucleation and growth process. Careful analysis of different systems reveals that ice strongly prefers to grow at (111) planes of cubic ice. This agrees with an earlier theoretical deduction based on considerations of water-ice interfacial energies. We find that ice nucleated by field bands usually grows as a mixture of cubic and hexagonal ice, consistent with other simulations of ice growth, and with experiment. This contrasts with simulations carried out with nucleating fields that span the entire surface area, where cubic ice dominates, and hexagonal layers are very rarely observed. We argue that this discrepancy is a simulation artifact related to finite sample size and periodic boundary conditions.