Mechanism of anisotropic surface self-diffusivity at the prismatic ice–vapor interface

Abstract

Predictive theoretical models for mesoscopic roughening of ice require improved understanding of attachment kinetics occurring at the ice-vapor interface. Here, we use classical molecular dynamics to explore the generality and mechanics of a transition from anisotropic to isotropic self-diffusivity on exposed prismatic surfaces. We find that self-diffusion parallel to the crystallographic a-axis is favored over the c-axis at sub-melt temperatures below about -35 °C, for three different representations of the water-water intermolecular potential. In the low-temperature anisotropic regime, diffusion results from interstitial admolecules encountering entropically distinct barriers to diffusion in the two in-plane directions. At higher temperatures, isotropic self-diffusion occurring deeper within the quasi-liquid layer becomes the dominant mechanism, owing to its larger energy of activation.

Hydrogen bonding and orientation effects on the accommodation of methylamine at the air-water interface

“…These two models represent one of the state of the art models for simulations of liquid water and ice using classical non-polarizable MD. 31,32,57,58 Moreover, the lower and higher values of free energy of hydration reported in Table I correspond for MA solvated in these water models. For all these reasons, these two models can provide us a good sample helping in drawing conclusions that can be as general as possible.…”

“…The presence of the lone pair sites is crucial to the resulting formation of the tetrahedral water arrangement, especially in solid phase. 31 It is for that reason that the TIP5P-Ew model is widely used in simulations of ice, 31,32 as it reproduces the exact melting temperature 33,34 and the water diffusivity within the supercool regime. 35 The structural and interaction parameters for these three models are reported in Table SII of the supplementary material.…”

A quasi‐liquid mediated continuum model of faceted ice dynamics

“…The initial physical dimensions of the simulation box were 4.49, 4.67, and 4.40 nm in the x , y , and z directions. The initial ice crystal was prepared according to standard procedures reported in detail in Gladich et al [, ]. A constant‐pressure simulation (NpT) was performed at 0 bar for 2.5 ns during which the ice crystal was heated linearly from 0 K to the target temperature of 260 K, which corresponds to about 29 K below the melting temperature of NE6 water [ Abascal et al , ].…”

“…Finally, starting from the ice/vapor slab, 20 ns of a constant volume ( NVT ) run was performed by using a time step of 2 fs at 260 K, resulting in the formation of quasi‐liquid layers at each ice/vapor interface after a few nanoseconds. The procedure described above has been shown to be a reliable protocol for simulation of ice interfaces using MD [ Girardet and Toubin , ; Muchová et al , ; Gladich and Roeselová , ; Gladich et al , ].…”

“…Finally, the geometry of the water molecules was constrained during all MD runs by using the SETTLE algorithm [ Miyamoto and Kollman , ]. This numerical setup is similar to that used in similar studies by using NE6, which has been shown to be numerically stable and conserve total energy [ Gladich et al , ; Pfalzgraff et al , ; Gladich et al , ].…”