Abstract
An accurate atomistic treatment of aqueous solid-liquid interfaces necessitates the explicit description of interfacial water ideally via ab initio molecular dynamics simulations. Many applications, however, still rely on static interfacial water models, e.g., for the computation of (electro)chemical reaction barriers and focus on a single, prototypical structure. In this work, we systematically study the relation between density functional theory-derived static and dynamic interfacial water models with specific focus on the water-Pt(111) interface. We first introduce a general construction protocol for static 2D water layers on any substrate, which we apply to the low indexsurfaces of Pt. Subsequently, we compare these with structures from a broad selection of reference works based on the Smooth Overlap of Atomic Positions descriptor. The analysis reveals some structural overlap between static and dynamic water ensembles; however, static structures tend to overemphasize the in-plane hydrogen bonding network. This feature is especially pronounced for the widely used low-temperature hexagonal ice-like structure. In addition, a complex relation between structure, work function, and adsorption energy is observed, which suggests that the concentration on single, static water models might introduce systematic biases that are likely reduced by averaging over consistently created structural ensembles, as introduced here.
Highlights
As the accurate description of electronic degrees of freedom and the chemical reactivity of the substrate are important, ab initio molecular dynamics (AIMD) results based on density functional theory (DFT) are the only reliable benchmarks to date
Structures with less hydrogen bonds, which mainly consist of chain-like water arrangements, fall in the region of AIMD results. These results indicate that ensemble averages based on 2D static water (2DSW) static water structures might approximate AIMD averages more accurately than using only selected low-temperature structural models
While all 2DSW water structures are provided alongside this work, we show a selection of three obtained structures in Fig. 3, 155, 194702-5
Summary
Solid–liquid interfaces (SLIs) are ubiquitous in nature, and their study is highly relevant for understanding the (electro)chemical transformation processes that lead to natural corrosion or (electro)catalytic applications, such as in batteries, electrolyzers, or fuel cells.[1,2,3,4,5,6] While liquid properties at distances larger than ∼1 nm from the interface are already bulk-like[7,8] and approximately described with standard continuum models,[9,10] the structure and composition of the first (few) solvent layers in contact with a solid surface typically show a significant dependence on, e.g., the solid substrate and the thermodynamic conditions, e.g., applied electrode potentials in electrochemistry contexts.[11,12,13,14,15,16,17,18,19] In aqueous solutions, an accurate atomistic treatment of the substrate–water interface necessitates the explicit inclusion of at least the first water layer for a wide range of properties such as adsorption energies or the potential of zero charge (PZC).[15,20,21,22,23] On the other hand, the sensitive dependence of these properties on the interfacial water structure[24,25,26,27] necessitates, in principle, an appropriate sampling of these to obtain reliable thermodynamic averages.[11,21,26,28,29] as the accurate description of electronic degrees of freedom and the chemical reactivity of the substrate are important, ab initio molecular dynamics (AIMD) results based on density functional theory (DFT) are the only reliable benchmarks to date. Latter structure comprises five, six, and seven water rings.[52–54] Such structures are typically less prominent in room temperature AIMD studies[16,50,56] where only (predominant) local water configurations can be identified.[16] This puts forward the question about the relation between theoretical results from static and dynamically sampled extended interfacial water structures and possible structural biases due to the dominant use of hexagonal water (bilayer) arrangements in applied works.[42,48,49]. We apply the algorithm to construct a dataset of 2D static water (2DSW) structures on low index Pt surfaces and compare the obtained structural ensemble of interfacial water with the structure of water layers from other reference works. One central aspect in this respect is the analysis of the relations between structure, adsorption energy, and work function reduction for Pt(111) with a single adsorbed water layer and as obtained from AIMD and our 2DSW ensemble. We find a decent overlap between AIMD and 2DSW ensemble averages, while single selected static models exhibit large variations in their predictive quality
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