Benchmarking water adsorption on metal surfaces with ab-initio molecular dynamics

Solid-water interfaces are ubiquitous in nature and technology. Particularly, in technologies evolving in the context of a green transition, such as electrochemistry, the junction of an electrolyte and an electrode is a central part of the device. Simulations based on density functional theory (DFT) have become de facto standard for both the understanding of atomistic processes at this interface and the screening for new materials. Thus, DFT's ability to simulate the solid/water interaction needs to be benchmarked and ideal simulation setups need to be identified, in order to prevent systematic errors. Here, we developed a rigorous sampling protocol for benchmarking the adsorption/desorption strength of water on metallic surfaces against experimental temperature programmed desorption, single crystal adsorption calorimetry and thermal energy atom scattering. We screened DFT's quality on a series of transition metal surfaces, applying three of the most common exchange correlation approximations; PBE-D3, RPBE-D3 and BEEF-vdW. We find that all three XC-functional reflect the pseudo-zeroth order desorption of water rooted in the combination of attractive adsorbate-adsorbate interactions at low coverages and their saturation at intermediate coverage. However, both RPBE-D3 and BEEF-vdW lead to more appropriate water binding strengths, while PBE-D3 clearly overbinds near-surface water. We are able to relate the variations in binding strength to specific variations in water-metal and water-water interactions, highlighting the structural consequences inherent in an uninformed choice of simulation parameters. Our study gives atomistic insight into the complex adsorption equilibrium of water and represents a guideline for future DFT-based simulations of the solvated solid interface within molecular dynamics studies by providing an assessment of systematic errors in specific setups.