Crystal orientation of epitaxial film deposited on silicon surface.

Direct growth of oxide film on silicon is usually prevented by extensive diffusion or chemical reaction between silicon (Si) and oxide materials. Thermodynamic stability of binary oxides is comprehensively investigated on Si substrates and shows possibility of chemical reaction of oxide materials on Si surface. However, the thermodynamic stability does not include any crystallographic factors, which is required for epitaxial growth.

Molecular Dynamics Study of the Microscopic Mechanical Balance at the Three-Phase Contact Line of Interfacial Nanobubble.

This study reveals the microscopic mechanical balance at the three-phase contact line (TPCL) of an interfacial nanobubble on a substrate with a wettability pattern using molecular dynamics simulations. The apparent contact angle was compared to that evaluated using Young's equation, in which the interfacial tensions were computed using a mechanical route. The comparison was conducted by changing the wettability of the substrate from hydrophilic to neutral while maintaining a hydrophobic region in the center of the substrate.

Deep Learning to Reveal the Distribution and Diffusion of Water Molecules in Fuel Cell Catalyst Layers.

Water management in the catalyst layers (CLs) of proton-exchange membrane fuel cells is crucial for its commercialization and popularization. However, the high experimental or computational cost in obtaining water distribution and diffusion remains a bottleneck in the existing experimental methods and simulation algorithms, and further mechanistic exploration at the nanoscale is necessary. Herein, we integrate, for the first time, molecular dynamics simulation with our customized analysis framework based on a multiattribute point cloud dataset and an advanced deep learning network.

Carbon clusters on substrate surface for graphene growth- theoretical and experimental approach.

Growth morphology of carbon clusters deposited on different substrates were investigated by theoretical and experimental approach. For theoretical approach, molecular dynamics was employed to evaluate an adsorptive stability of different size of carbon clusters placed on different substrates. The adsorptive stability was estimated by the difference of total energy of supercell designed as carbon cluster placed on a certain crystal plane of substrate.

Prediction of nanoscale thermal transport and adsorption of liquid containing surfactant at solid-liquid interface via deep learning.

Hypothesis: Recent advances in deep learning (DL) have enabled high level of real-time prediction of thermophysical properties of materials. On the other hand, molecular dynamics (MD) have been long used as a numerical microscope to observe detailed interfacial conditions but require separate simulations that are computationally costly. Hence, it should be possible to combine MD and DL to obtain high resolution interfacial details at a low computational cost.

Molecular Dynamics Study of Ion Transport in Polymer Electrolytes of All-Solid-State Li-Ion Batteries.

Atomistic analysis of the ion transport in polymer electrolytes for all-solid-state Li-ion batteries was performed using molecular dynamics simulations to investigate the relationship between Li-ion transport and polymer morphology. Polyethylene oxide (PEO) and poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), were used as the electrolyte materials, and the effects of salt concentrations and polymer types on the ion transport properties were explored. The size and number of LiTFSI clusters were found to increase with increasing salt concentrations, leading to a decrease in ion diffusivity at high salt concentrations.

Ab initio studies of the effect of the fluorination on deprotonation reaction of the benzene sulfonic acid.

We carried out quantum chemical calculations to analyze the effects of fluorination on the activation energy (Ea) of sulfonic group deprotonation by water molecules. The model molecule was 2,3,4,5,6-pentafluorobenzenesulfonic acid (5FBSA), which was obtained by substituting all aromatic hydrogen atoms of benzenesulfonic acid (BSA) for fluorine atoms. The target hydration level was three.

Relationship between Proton Transport and Morphology of Perfluorosulfonic Acid Membranes: A Reactive Molecular Dynamics Approach.

A reactive molecular dynamics simulation has been performed for the characterization of the relationship between proton transport and water clustering in polymer electrolyte membranes. We have demonstrated that the anharmonic two-state empirical valence bond model is capable of describing efficiently excess proton transport through the Grotthuss hopping mechanism within the simplicity of the theoretical framework. To explore the long-time diffusion behavior in perfluorosulfonic acid membranes with statistical certainty, simulations that are longer than 10 ns are needed.

Molecular Dynamics Study for Channel Size Dependence of Shear Stress Between Droplet and Wall.

In this study, the channel size dependence of the shear stress between water droplets and solid walls in nm-order channel was analyzed. We considered a several different-sized and highly hydrophobic channel whose macroscopic contact angle was about 150 degrees. We have evaluated the shear stress and the normal pressure by molecular dynamics simulation.

Extraction of the Density Fluctuations in Diatomic Fluids Around the Critical Points Using Molecular Dynamics Simulation.

The objective in this study is the investigation of the principle of corresponding state for the density fluctuation around the critical points of non-polar diatomic fluids. In this paper, we conducted Molecular Dynamics (MD) simulation for the extraction of the fluctuation structure around the critical points of 2-Center-Lennard-Jones (2CLJ) fluids, which have anisotropy depending on the molecular elongation. As a result, in the 2CLJ fluids which have comparatively shorter molecular elongations, the principle of corresponding state can be satisfied because almost all density fluctuations in each elongation showed the similar values.

Molecular Dynamics Simulation of Proton Transport in Polymer Electrolyte Membrane.

We have performed a detailed analysis of proton solvation and transport properties in hydrated Nafion using molecular dynamics simulation. The revised empirical valence bond (EVB) method was developed in order to treat the excess proton transport through the Grotthuss mechanism. The new EVB model predicts a significantly enhanced transport in comparison with previous hopping models as well as the classical hydronium diffusion, which largely improves the agreement with the available experimental data.

A modified two-state empirical valence bond model for proton transport in aqueous solutions.

A detailed analysis of the proton solvation structure and transport properties in aqueous solutions is performed using classical molecular dynamics simulations. A refined two-state empirical valence bond (aTS-EVB) method, which is based on the EVB model of Walbran and Kornyshev and the anharmonic water force field, is developed in order to describe efficiently excess proton transport via the Grotthuss mechanism. The new aTS-EVB model clearly satisfies the requirement for simpler and faster calculation, because of the simplicity of the two-state EVB algorithm, while providing a better description of diffusive dynamics of the excess proton and water in comparison with the previous two-state EVB models, which significantly improves agreement with the available experimental data.

Effect of bound state of water on hydronium ion mobility in hydrated Nafion using molecular dynamics simulations.

We have performed a detailed analysis of the structural properties of the sulfonate groups in terms of isolated and overlapped solvation shells in the nanostructure of hydrated Nafion membrane using classical molecular dynamics simulations. Our simulations have demonstrated the correlation between the two different areas in bound water region, i.e.

Reaction analysis for deprotonation of the sulfonic group of perfluorosulfonic acid molecules at low hydration levels.

A reaction analysis for deprotonation of the sulfonic group in a model molecule of perfluorosulfonic acid (PFSA) at low hydration levels was performed. PFSA is usually adopted as a polymer electrolyte membrane in polymer electrolyte fuel cells. In hydration level three, the deprotonation reaction certainly occurs.

Bottom-up construction of interaction models of non-Markovian dissipative particle dynamics.

We derive the equation of motion for non-Markovian dissipative particle dynamics (NMDPD) by introducing the history effects on the time evolution of the system. Our formulation is based on the generalized Langevin equation, which describes the motions of the centers of mass of clusters comprising microscopic particles. The mean, friction, and fluctuating forces in the NMDPD model are directly constructed from an underlying molecular dynamics (MD) system without any scaling procedure.

Energy dissipation in non-isothermal molecular dynamics simulations of confined liquids under shear.

Energy is commonly dissipated in molecular dynamics simulations by using a thermostat. In non-isothermal shear simulations of confined liquids, the choice of the thermostat is very delicate. We show in this paper that under certain conditions, the use of classical thermostats can lead to an erroneous description of the dynamics in the confined system.