Stabilization of AgI's polar surfaces by the aqueous environment, and its implications for ice formation

Abstract

Silver iodide is one of the most potent inorganic ice nucleating particles known, a feature generally attributed to the excellent lattice match between its basal Ag-(0 0 0 1) and I-(0 0 0 1) surfaces, and ice. This crystal termination, however, is a type-III polar surface, and its surface energy therefore diverges with crystal size unless a polarity compensation mechanism prevails. In this simulation study, we investigate to what extent the surrounding aqueous environment is able to provide such polarity compensation. On its own, we find that pure H 2 O is unable to stabilize the AgI crystal in a physically reasonable manner, and that mobile charge carriers such as dissolved ions, are essential. In other words, proximate dissolved ions must be considered an integral part of the heterogeneous ice formation mechanism. The simulations we perform utilize recent advances in simulation methodology in which appropriate electric and electric displacement fields are imposed. A useful by-product of this study is the direct comparison to the commonly used Yeh-Berkowitz method that this enables. Here we find that naive application of the latter leads to physically unreasonable results, and greatly influences the structure of H 2 O in the contact layer. We therefore expect these results to be of general importance to those studying polar/charged surfaces in aqueous environments. arXiv:2006.12026v1 [cond-mat.mtrl-sci]

Atomistic and coarse grained simulations reveal increased ice nucleation activity on silver iodide surfaces in slit and wedge geometries

“…The microscopic growth mechanisms are discussed in more detail in section 4.4. To quantify the enhancement of ice nucleation in confined wedge geometries, we compare our results to simulations on the flat AgI (0001) surface, which has been extensively studied using the TIP4P/Ice water model (Fraux and Doye, 2014;Zielke et al, 2014Zielke et al, , 2015Glatz and Sarupria, 2016;Sayer and Cox, 2019;Roudsari et al, 2020). Our results with the TIP4P/Ice model show a high nucleation rate at 263 K, consistent with previous work, but no nucleation at 265 K or 267 K at timescales easily accessible with direct MD simulations.…”

Atomistic Simulation of Ice Nucleation on Silver Iodide (0001) Surfaces with Defects

“…However, AgI (0001) is a type 3 polar surface, 13 and therefore intrinsically unstable. While a recent study showed that the interface with an aqueous solution can stabilise the (0001) surface, 14 reconstructions and defects are still expected to be abundant, as can be seen from electron microscope images of micrometer-sized AgI plate crystals exposing (0001) facets. 15 It is therefore important to investigate how the presence of such defects on AgI (0001) surfaces affects ice nucleation and growth rates.…”

Macroscopic surface charges from microscopic simulations

“…[8][9][10][11][12] The purpose of this article is to demonstrate how commonly used simulation approaches lead to qualitatively incorrect descriptions of ion adsorption at charged interfaces. We will also extend the ideas of previous works [12][13][14][15] to not only correct for small system sizes, but to understand why other methods fail in a dramatic fashion. In fact, this simply amounts to setting the electrostatic boundary conditions appropriately; as this is relatively straightforward to do in existing simulation packages, 16 it is hoped that the results presented herealong with those in Refs.…”

“…It is well established that such polar crystal terminations are inherently unstable, and rea) Electronic mail: sjc236@cam.ac.uk quire a polarity compensation mechanism. 15,[17][18][19][20] In this article, we will focus on the case where adsorption of charge from the external environment stabilizes the crystal. Specifically, we expect counterions from solution to adsorb to the crystal's surfaces such that the integrated charge density over an interfacial region, e.g.,…”