Density functional theory study of catalytic reaction at interfacial boundaries and molecular dynamics study on relaxations in viscous fluids

Abstract

The mechanism of grain boundary-mediated electrochemical carbon dioxide ($CO_{2}$) reduction is studied using extensive density functional theory (DFT) calculations. Electrochemical carbon dioxide reduction is an emerging technology for efficiently recycling $CO_{2}$ into fuel, and many studies of this reaction are focused on developing advanced catalysts with high activity, selectivity, and durability. Of these catalysts, oxide-derived metal nanoparticles, which are prepared by reducing a metal oxide, have received considerable attention due to their catalytic properties. Recently, it was discovered that the catalytic activity is quantitatively correlated to the surface density of grain boundaries (GBs), implying that GBs are mechanistically important in electrochemical $CO_{2}$ reduction. Here, using DFT calculations modeling the atomistic structure of GBs on the Au (111) surface, we suggest a mechanism of electrochemical $CO_{2}$ reduction to CO mediated by GBs

the broken local spatial symmetry near a GB tunes the Au metal-to-adsorbate $\pi$-backbonding ability, thereby stabilizing the key COOH intermediate.

The nature of intrinsic uncertainties, statistical errors and system size effects, in estimating shear viscosity via equilibrium molecular dynamics (MD) simulations are investigated using simple and complex fluid models. Uncertainty quantification formulas for the statistical errors in the shear-stress autocorrelation function (SACF) and shear viscosity are obtained under the assumption that shear stress follows a Gaussian process. Comparison with the simulation results for diffusion process reveals that the Gaussianity is more pronounced in the shear-stress process (related to shear viscosity estimation) compared with the velocity process of an individual molecule (related to self-diffusion coefficient). At relatively high densities corresponding to a liquid state, the shear viscosity exhibits complex size-dependent behavior unless the system is larger than a certain length scale. Whereas, its size-dependent behavior is characterized by a scaling behavior with $L^{-1}$ correction term at relatively low density. Analysis on the potential contribution in the SACF reveals that the former is \emph{configurational} and is attributed to the poor description of the long-range spatial correlations in finite systems. Further analysis on the kinetic counterpart reveal that the latter has a \emph{hydrodynamic} nature. The $L^{-1}$ correction term of shear viscosity is described using an empirical formula based on hydrodynamic equations.