Effect of Surface Chemistry on Water Interaction with Cu(111)

Differences in solvation thermodynamics of oxygenates at Pt/Al2O3 perimeter versus Pt(111) terrace sites

A prominent role of water in aqueous-phase heterogeneous catalysis is to modify free energies; however, intuition about how is based largely on pure metal surfaces or even homogeneous solutions. Using multiscale modeling with explicit liquid water molecules, we show that the influence of water on the free energies of adsorbates at metal/support interfaces is different than that on pure metal surfaces. We specifically compute free energies of solvation for methanol and its constituents on a Pt/Al2O3 catalyst and compare the results to analogous values calculated on a pure Pt catalyst. We find that the more hydrophilic Pt/Al2O3 interface leads to smaller (more positive) free energies of solvation due to an increased entropy penalty resulting from the additional work necessary to disrupt the interfacial water structure and accommodate the interfacial species. The results will be of interest in other fields, including adsorption and proteins.

Optimized utilization of COMB3 reactive potentials in LAMMPS

An investigation to optimize the application of the third-generation charge optimized many-body (COMB3) interatomic potential and associated input parameters was carried out through the study of solid-liquid interactions in classical molecular dynamics simulations. The rates of these molecular interactions are understood through the wetting rates of water nano-droplets on a bare copper (111) surface. Implementing the Langevin thermostat, the influence of simulation time step, the number of atoms in the system, the frequency at which charge equilibration is performed, and the temperature relaxation rate are all examined. The results indicate that time steps of 0.4 fs are possible when using longer relaxation times for the system temperature, which is almost double the typical time step used for reactive potentials. The use of the charge equilibration allows for a fewer atomic layers to be used in the Cu slab. In addition, charge equilibrium schemes do not need to be performed every time step to ensure accurate charge transfer. Interestingly, the rate of wetting for the nanodroplets is dominantly dependent on the temperature relaxation time, which is predicted to significantly change the viscosity of the water droplets. This work provides a pathway for optimizing simulations using the COMB3 reactive interatomic potential.

Nanoscale Structure and Dynamics of Water on Pt and Cu Surfaces from MD Simulations

The interaction of liquid water with Pt(111) is investigated with classical molecular dynamics (MD) simulations, where the forces are determined using the third-generation charge optimized many-body (COMB3) interatomic potential. In cases of sub-monolayer water coverage, the parameterized empirical potential predicts experimentally observed and energetically favorable √37 and √39 reconstructed water structures with "575757" di-interstitial defects. At both sub-monolayer and multilayer water coverages, the structure of the first wetting layer of liquid water on Pt(111) exhibits a characteristic distribution where the molecules form two distinct buckled layers as a result of the interplay between water-metal adsorption and water-water hydrogen bonds. The dynamic spreading rate of water nanodroplets on large Pt surfaces (>200 nm²) characterized by molecular kinetic spreading theory is an order of magnitude slower than the molecular kinetic rate of the same droplet on close-packed Cu surfaces due to variation in molecular distributions at the water-metal interface. These nanoscale MD simulation predictions using the COMB3 interatomic potential demonstrate the capability of capturing both many-body interactions between H₂O and Pt or Cu and hydrogen bonding in liquid water.

Charge optimized many body (COMB) potentials for Pt and Au

Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress-strain behaviour is investigated and the primary slip systems {1 1 1}〈1 [Formula: see text] 0〉 are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of [Formula: see text] eV for Pt and [Formula: see text] eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.