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The shape, size, and compositionof catalyst nanoparticles canhave a significant influence on catalytic activity. Understandingsuch structure–reactivity relationships is crucial for theoptimization of industrial catalysts and the design of novel catalystswith enhanced properties. In this letter, we employ a combinationof first-principles computations and large-scale Monte-Carlo simulationswith highly accurate neural network potentials to study the equilibriumsurface structure and composition of bimetallic Au/Cu nanoparticles(NPs), which have recently been of interest as stable and efficientCO2reduction catalysts. We demonstrate that the inclusionof explicit water molecules at a first-principles level of accuracyis necessary to predict experimentally observed trends in Au/Cu NPsurface composition; in particular, we find that Au-coated core–shellNPs are thermodynamically favored in vacuum, independent of Au/Cuchemical potential and NP size, while NPs with mixed Au–Cusurfaces are preferred in aqueous solution. Furthermore, we show thatboth CO and O2adsorption energies differ significantlyfor NPs with the equilibrium surface composition found in water andthose with the equilibrium surface composition found in vacuum, suggestinglarge changes in CO2reduction activity. Our results emphasizethe importance of understanding and being able to predict the effectsof catalytic environment on catalyst structure and activity. In addition,they demonstrate that first-principles-based neural network potentialsprovide a promising approach for accurately investigating the relationshipsbetween solvent, surface composition and morphology, surface electronicstructure, and catalytic activity in systems composed of thousandsof atoms. [ABSTRACT FROM AUTHOR]

We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate (BaTiO3) nanowires. Variable-temperature electrostatic force microscopy is used to manipulate, image, and evaluate the diameter-dependent stability of ferroelectric polarizations. These measurements show that the ferroelectric phase transition temperature (TC) is depressed as the nanowire diameter (dnw) decreases, following a 1/dnw scaling. The diameter at which TC falls below room temperature is determined to be ∼3 nm, and extrapolation of the data indicates that nanowires with dnw as small as 0.8 nm can support ferroelectricity at lower temperatures. We also present density functional theory (DFT) calculations of bare and molecule-covered BaTiO3 surfaces. These calculations indicate that ferroelectricity in nanowires is stabilized by molecular adsorbates such as OH and carboxylates. These adsorbates are found to passivate polarization charge more effectively than metallic electrodes, explaining the observed stability of ferroelectricity in small-diameter BaTiO3 nanowires. [ABSTRACT FROM AUTHOR]