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Results for “COMB3”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Dynamics of graphene/Al interfaces using COMB3 potentials

This paper describes the development of a third-generation charge optimized many-body (COMB3) potential for Al-C and its application to the investigation of aluminum/graphene nanostructures. In particular, the new COMB3 potential was used to investigate the interactions of aluminum surfaces with pristine and defective graphene sheets. Classical molecular dynamics simulations were performed at temperatures of 300–900 K to investigate the structural evolution of these interfaces. In this work, the results indicate that, although the interfaces between Al and graphene are mostly weakly bonded, aluminum carbide can form under the right conditions, including the presence of vacancy defects in graphene, undercoordinated Al in surface regions with sharp boundaries, and at high temperatures. COMB3 potentials were further used to examine a new method to transfer graphene between Al surfaces as well as between Al and Cu surfaces by controlling the angle of graphene between the two surfaces. The findings indicate that, by controlling the peeling angles, it is possible to transfer graphene without any damage from the surface having greater graphene/surface adhesion to another surface with less adhesion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

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. Additionally, 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.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effects of surface charge and cluster size on the electrochemical dissolution of platinum nanoparticles using COMB3 and continuum electrolyte models

We study the site-dependent dissolution of platinum nanoparticles under electrochemical conditions to assess their thermodynamic stability as a function of shape and size using empirical molecular dynamics and electronic-structure models. The third-generation charge optimized many-body potential is employed to determine the validity of uniform spherical representations of the nanoparticles in predicting dissolution potentials (the Kelvin model). To understand the early stages of catalyst dissolution, implicit solvation techniques based on the self-consistent continuum solvation method are applied. It is demonstrated that interfacial charge and polarization can shift the dissolution energies by amounts on the order of 0.74 eV depending on the surface site and nanoparticle shape, leading to the unexpected preferential removal of platinum cations from highly coordinated sites in some cases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Dynamical properties of AlN nanostructures and heterogeneous interfaces predicted using COMB potentials

A new empirical variable charge potential has been developed for AlN within the third-generation charge optimized many-body (COMB3) potential framework. We report the potential is able to reproduce the fundamental physical properties of AlN, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of AlN obtained from experiments and first-principles calculations. The thermodynamic properties of the Al(1 1 1)-AlN ( 1 0 1 ¯ 0 ) and Al 2 O 3 (0 0 0 1)-AlN ( 1 0 1 ¯ 0 ) interfaces and the tensile response of AlN nanowires and nanotubes are investigated in classical molecular dynamical (MD) simulations using this COMB3 potential. The results demonstrate that the potential is well suited to model heterogeneous materials in the Al–O–N system. Most importantly, the fully transferrable potential parameters can be seamlessly coupled with existing COMB3 parameters of other elements to enable MD simulations for an even wider range of heterogeneous materials systems.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Probing the accuracy of reactive and non-reactive force fields to describe physical and chemical properties of graphene-oxide

Graphene-oxide (GO) has been shown to be a promising material for numerous technological applications. Extensive computational work has been devoted to elucidate the structure, stability and properties of different GO species. As some applications require large GO sizes, classical molecular dynamics simulations are necessary to fully investigate GO properties and behavior. There are few classical force fields parameterized to examine oxidized hydrocarbon compounds, and not all of them are able to simulate GO structures. Here, we present the first comparative study of some GO properties between three classical force fields: Reactive Empirical Bond Order for carbon, hydrogen and oxygen (REBO-CHO), third generation of the Charge Optimized Many Body (COMB3) and Chemistry at HARvard Macromolecular Mechanics (CHARMM) force field. The chemical and physical properties tested include key binding energies, carbon–oxygen bond distances and elastic modulus. Lastly, when compared to density functional theory calculations or experimental data, the COMB3 reactive force field is shown to provide the best overall results, while REBO-CHO and CHARMM provide good results for certain properties of most GO-systems.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic-scale modeling of the dissolution of oxidized platinum nanoparticles in an explicit water environment

Pt nanoparticles (NPs) are currently being investigated for use in fuel cells; however, Pt NP oxidation as a function of size, morphology, and temperature is not well understood or currently quantified. In this study, the stability and dissolution of oxidized platinum NPs is examined via classical molecular dynamics in an explicit water environment. The NPs considered range in size from 1.35 to 2.92 nm in diameter and included five different monolayer (ML) coverages of O*. The simulations were performed at 300, 450, and 600 K with the many-body, reactive third-generation charge-optimized many-body or COMB3 potentials and examine the kinetics of NP dissolution in water. The Pt–O layer, which reduces the kinetic activity for Pt atom dissolution, is projected to make dissolution more favorable for O* MLs smaller than 0.5. The simulations further indicate that the Pt NPs' kinetic rates of dissolution are slowed by an increase in the number of adsorbed species caused by the dissociation of water molecules at the reconstructed facets of the Pt NPs. Furthermore, these findings quantify the effect of oxygen and temperature on the stability and dissolution of oxidized platinum NP in an explicit water environment similar to the conditions in fuel cells and electrocatalysis.

08 HYDROGEN↗
DOE OSTI2018

Titanium-Carbide Formation at Defective Curved Graphene-Titanium Interfaces

ABSTRACT Physical and chemical properties of graphene-metal interfaces have been largely examined with the objective of producing nanostructured carbon-based electronic devices. Although electronic properties are key to such devices, appropriate structural, thermal and mechanical properties are important for device performance as well. One of the most studied is the graphene-titanium (G-Ti) interface. Titanium is a low density, high strength versatile metal that can form alloys with desirable properties for applications ranging from aerospace to medicine. Small clusters and thin films of titanium deposited on graphene have also been examined. However, while some experiments show that thin films of titanium on graphene can be removed without damaging graphene hexagonal structure, others reported the formation of titanium-carbide (TiC) at G-Ti interfaces. In a previous work [ACS Appl. Mater. Interfaces, 2017, 9 (38), pp 33288-33297], we have shown that pristine G-Ti interfaces are resilient to large thermal fluctuations even when G-Ti structures lie on curved or kinked substrates. Here, using classical molecular dynamics with the third-generation Charge Optimized Many Body (COMB3) potential, we show that di-interstitial defective G-Ti structures on a copper substrate with a relatively large curvature kink, present signs of TiC formation. This result might help explain the different experimental results mentioned above.

catalysis (heterogeneous), defects, membrane, carb↗
DOE OSTI2017

Graphene–Titanium Interfaces from Molecular Dynamics Simulations

Unraveling the physical and chemical properties of graphene–metal contacts is a key step toward the development of graphitic electronic nanodevices. Although many studies have revealed the way that various metals interact with graphene, few have described the structure and behavior of large pieces of graphene–metal nanostructures under different conditions. In this paper, we present the first classical molecular dynamics study of graphene–titanium (G–Ti) structures, with and without substrates. Physical and chemical properties of equilibrium structures of G–Ti interfaces with different amounts of titanium coverage are investigated. Adhesion of Ti films on graphene is shown to be enhanced by the vacancies in graphene or the electrostatic influence of substrates. The dynamics of pristine G–Ti structures at different temperatures on planar and nonplanar substrates are investigated, and the results show that G–Ti interfaces are thermally stable, that is, not prone to any reaction toward the formation of titanium carbide.

36 MATERIALS SCIENCE↗