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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Application of a New Ensemble Conserving Quantum Dynamics Simulation Algorithm to Liquid para-Hydrogen and ortho-Deuterium

Here, we apply the Feynman-Kleinert Quasi-Classical Wigner (FK-QCW) method developed in our previous work [Smith et al., J. Chem. Phys. 142, 244112 (2015)] for the determination of the dynamic structure factor of liquid para-hydrogen and ortho-deuterium at state points of (T = 20.0 K, n = 21.24 nm -3 ) and (T = 23.0 K, n = 24.61 nm -3 ), respectively. When applied to this challenging system, it is shown that this new FK-QCW method consistently reproduces the experimental dynamic structure factor reported by Smith et al. [J. Chem. Phys. 140, 034501 (2014)] for all momentum transfers considered. Moreover, this shows that FK-QCW provides a substantial improvement over the Feynman-Kleinert linearized path-integral method, in which purely classical dynamics are used. Furthermore, for small momentum transfers, it is shown that FK-QCW provides nearly the same results as ring-polymer molecular dynamics (RPMD), thus suggesting that FK-QCW provides a potentially more appealing algorithm than RPMD since it is not formally limited to correlation functions involving linear operators.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Molecular dynamics simulation of sodium aluminosilicate glass structures and glass surface-water reactions using the reactive force field (ReaxFF)

Reactive potentials are increasingly used to study the properties of glasses and glass water reactions in a reactive molecular dynamics (MD) framework. In this study, we have simulated a ternary sodium aluminosilicate glass and investigated the initial stages of the glass surface-water reactions at 300 K using reactive force field (ReaxFF). On comparison of the simulated glass structures generated using ReaxFF and classical Buckingham potentials, our results show that the atomic density profiles calculated for the surface glass structures indicate a bond-angle distribution dependency. The atomic density profiles also show higher concentrations of non-bridging oxygens (NBOs) and sodium ions at the glass surface. Additionally, we present our results of formation of silanol species and the diffusion of water molecules at the glass surface using ReaxFF.

Chemistry↗
DOE OSTI2017

Faster than Real-Time Dynamic Simulation for Large-Size Power System with Detailed Dynamic Models using High-Performance Computing Platform

This paper presents a faster-than-real-time dynamic simulation software package that is designed for large-size power system dynamic simulation. It was developed on the GridPACKTM high-performance computing (HPC) framework. The key features of the developed software package include (1) faster-than-real-time dynamic simulation for a WECC system (17,000 buses) with different types of detailed generator, controller, and relay dynamic models, (2) a decoupled parallel dynamic simulation algorithm with optimized computation architecture to better leverage HPC resources and technologies, (3) options for HPC-based linear and iterative solvers, (4) hidden HPC details, such as data communication and distribution, to enable development centered on mathematical models and algorithms rather than on computational details for power system researchers, and (5) easy integration of new dynamic models and related algorithms into the software package.

Huang, Renke↗
DOE OSTI2018

Beyond the standard two-film theory: Computational fluid dynamics simulations for carbon dioxide capture in a wetted wall column

The standard two-film theory (STFT) is a diffusion-based mechanism that can be used to describe gas mass transfer across liquid film. Fundamental assumptions of the STFT impose serious limitations on its ability to predict mass transfer coefficients. To better understand gas absorption across liquid film in practical situations, a multiphase computational fluid dynamics (CFD) model fully equipped with mass transport and chemistry capabilities has been developed for solvent-based carbon dioxide (CO2) capture to predict the CO2 mass transfer coefficient in a wetted wall column. The hydrodynamics is modeled using a volume of fluid method, and the diffusive and reactive mass transfer between the two phases is modeled by adopting a one-fluid formulation. We demonstrate that the proposed CFD model can naturally account for the influence of many important factors on the overall mass transfer that cannot be quantitatively explained by the STFT, such as the local variation in fluid velocities and properties, flow instabilities, and complex geometries. The CFD model also can predict the local mass transfer coefficient variation along the column height, which the STFT typically does not consider.

Wang, Chao↗
DOE OSTI2016

Excited Electron Dynamics at Semiconductor–Molecule Type-II Heterojunction Interface: First-Principles Dynamics Simulation

Excited electron dynamics at semiconductor–molecule interfaces is ubiquitous in various energy conversion technologies. However, a quantitative understanding of how molecular details influence the quantum dynamics of excited electrons remains a great scientific challenge because of the complex interplay of different processes with various time scales. Here in this paper, we employ first-principles electron dynamics simulations to investigate how molecular features govern the dynamics in a representative interface between the hydrogen-terminated Si(111) surface and a cyanidin molecule. Hot electron transfer to the chemisorbed molecule was observed but was short-lived on the molecule. Interfacial electron transfer to the chemisorbed molecule was found to be largely decoupled from hot electron relaxation within the semiconductor surface. While the hot electron relaxation was found to take place on a time scale of several hundred femtoseconds, the subsequent interfacial electron transfer was slower by an order of magnitude. Finally, at the same time, this secondary process of picosecond electron transfer is comparable in time scale to typical electron trapping into defect states in the energy gap.

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

Molecular Dynamics Simulation of the Structures, Dynamics, and Aggregation of Dissolved Organic Matter

Dissolved organic matter (DOM) plays a significant role in the transport and transformation of pollutants in the aquatic environment. However, the experimental characterization of DOM has been limited mainly to bulk properties, and the molecular-level interactions among various components of DOM remain to be fully characterized. In this study, we use molecular dynamics (MD) simulations to probe the structural properties of model DOM systems at atomic detail. The 200 ns simulations, validated by available experimental data, reveal processes and mechanisms by which chemical species (cations, peptides, lipids, lignin, carbohydrates, and some low-molecular-weight aliphatic and aromatic compounds) aggregate to form complex DOM. The DOM aggregates are dynamic, consisting of a hydrophobic core and amphiphilic exterior. The lipid tails and other hydrophobic fragments form the core, with hydrophilic and amphiphilic groups exposed to water, making DOM accessible to both polar and nonpolar species. Thus, the lipid component acts as a nucleator, whereas cations (especially Ca 2+ ) connect the molecular fragments on the surface by coordinating with the O-containing functional groups of DOM. The structural details revealed here provide new insights including surface accessible atoms, overall assemblage, and interactions among the molecules of DOM for understanding the kinetics and mechanisms through which DOM interacts with metal and other contaminants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Structure, solvation, and dynamics of Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, and Ba{sup 2+} complexes with 3-hydroxyflavone and perchlorate anion in acetonitrile medium: A molecular dynamics simulation study

Molecular dynamics simulations of complexes of Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, and Ba{sup 2+} with 3-hydroxyflavone (flavonol, 3HF) and ClO {sub 4}{sup −} in acetonitrile were performed. The united atoms force field model was proposed for the 3HF molecule using the results of DFT quantum chemical calculations. 3HF was interpreted as a rigid molecule with two internal degrees of freedom, i.e., rotation of the phenyl ring and of the OH group with respect to the chromone moiety. The interatomic radial distribution functions showed that interaction of the cations with flavonol occurs via the carbonyl group of 3HF and it is accompanied with substitution of one of the acetonitrile molecules in the cations’ first solvation shells. Formation of the cation–3HF complexes does not have significant impact on the rotation of the phenyl ring with respect to the chromone moiety. However, the orientation of the flavonol's OH-group is more sensitive to the interaction with doubly charged cations. When complex with Mg{sup 2+} is formed, the OH-group turns out of the plane of the chromone moiety that leads to rupture of intramolecular H-bond in the ligand molecule. Complexation of Ca{sup 2+}, Sr{sup 2+}, and BaClO {sub 4}{sup +} with 3HF produces two structures with different OH-positions, as in the free flavonol with the intramolecular H-bond and as in the complex with Mg{sup 2+} with disrupted H-bonding. It was shown that additional stabilization of the [MgClO{sub 4}(3HF)]{sup +} and [BaClO{sub 4}(3HF)]{sup +} complexes is determined by strong affinity of perchlorate anion to interact with flavonol via intracomplex hydrogen bond between an oxygen atom of the anion and the hydrogen atom of the 3-hydroxyl group. Noticeable difference in the values of the self-diffusion coefficients for Kt{sup 2+} from one side and ClO {sub 4}{sup −}, 3HF, and AN in the cations’ coordination shell from another side implies quite weak interaction between cation, anion, and ligands in the investigated complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The alloying element dependence of the local lattice deformation and the elastic properties of Ni{sub 3}Al: A molecular dynamics simulation

Molecular dynamics (MD) together with the modified analytical embedded atom method (MAEAM) is employed to study the alloying elements (Re, Ru, Co, and Ta) dependence of the elastic properties of L1{sub 2}-Ni{sub 3}Al. The investigations indicate that the calculated elastic properties of Ni{sub 3}Al are in reasonable agreement with the previous results. The substituting formation energies of the alloying elements in Ni{sub 3}Al are calculated to determine the site preference. It is found out that Re, Ru, and Ta atoms prefer to occupy the Al sites, and the Co atom prefers to occupy the Ni site. Based on Re, Ru, and Ta substituting the 1st, 2nd, 3rd, and 4th nearest-neighbor atoms, we ascertain that the substituting manners of these alloying elements have a decisive effect on the bulk modulus and the local crystal lattice of Ni{sub 3}Al. Moreover, for Re, the bonding interaction plays a predominant role in the improvement in the bulk modulus of Ni{sub 3}Al, whereas the size effect of Ru and Ta on the improvement in the bulk modulus is more obvious. Finally, the potential reasons of which the alloying elements enhance the bulk modulus are discussed in details.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Predicting 1 H NMR relaxation in Gd 3+ -aqua using molecular dynamics simulations

Atomistic molecular dynamics simulations are used to predict 1 H NMR T 1 relaxation of water from paramagnetic Gd 3+ ions in solution at 25 °C. Simulations of the T 1 relaxivity dispersion function r 1 computed from the Gd 3+ – 1 H dipole–dipole autocorrelation function agree within ≃8% of measurements in the range f 0 ≃ 5 ↔ 500 MHz, without any adjustable parameters in the interpretation of the simulations, and without any relaxation models. Here the simulation results are discussed in the context of the Solomon-Bloembergen-Morgan inner-sphere relaxation model, and the Hwang-Freed outer-sphere relaxation model. Below f 0 ≲ 5 MHz, the simulation overestimates r 1 compared to measurements, which is used to estimate the zero-field electron-spin relaxation time. The simulations show potential for predicting r 1 at high frequencies in chelated Gd 3+ contrast-agents used for clinical MRI.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Interfaces of dicationic ionic liquids and graphene: a molecular dynamics simulation study

Molecular dynamics simulations were performed to investigate the interfacial structure and capacitance of electrical double layers (EDLs) in dicationic ionic liquids (DILs) 1-alkyl-3-dimethylimidazolium tetrafluoroborate [Cn(mim)2](BF4)2 (n = 3, 6, 9), with respect to a baseline of a monocationic ionic liquid [C3mim][BF4], near planar carbon electrodes consisting of graphene sheets. The simulation results show that an adsorbed layer with double peaks is exclusively found for [C3(mim)2](BF4)2, while a single peak of the other three cations is observed at the neutral electrode, due to the difference in ion–wall interaction and cation–anion association. As the electrode becomes negatively charged, the second peak of [C3(mim)2]2+ is dramatically reduced, whereas those of [C6(mim)2]2+ and [C9(mim)2]2+ become non-trivial. The capacitance–potential curve of EDLs in DILs manifests a transition from camel shape to bell shape as the cation chain length increases, which is attributed to the enlargement of ion adsorption (per unit charge) on the electrode and the decrease of attractive interaction between ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Photodissociation dynamics of CH{sub 3}C(O)SH in argon matrix: A QM/MM nonadiabatic dynamics simulation

In this work, we have first employed the combined quantum mechanics/molecular mechanics (QM/MM) method to study the photodissociation mechanism of thioacetic acid CH{sub 3}C(O)SH in the S{sub 1}, T{sub 1}, and S{sub 0} states in argon matrix. CH{sub 3}C(O)SH is treated quantum mechanically using the complete active space self-consistent field and complete active space second-order perturbation theory methods; argon matrix is described classically using Lennard-Jones potentials. We find that the C-S bond fission is predominant due to its small barriers of ca. 3.0 and 1.0 kcal/mol in the S{sub 1} and T{sub 1} states. It completely suppresses the nearby C—C bond fission. After the bond fission, the S{sub 1} radical pair of CH{sub 3}CO and SH can decay to the S{sub 0} and T{sub 1} states via internal conversion and intersystem crossing, respectively. In the S{sub 0} state, the radical pair can either recombine to form CH{sub 3}C(O)SH or proceed to form molecular products of CH{sub 2}CO and H{sub 2}S. We have further employed our recently developed QM/MM generalized trajectory-based surface-hopping method to simulate the photodissociation dynamics of CH{sub 3}C(O)SH. In 1 ps dynamics simulation, 56% trajectories stay at the Franck-Condon region; the S{sub 1} C—S bond fission takes place in the remaining 44% trajectories. Among all nonadiabatic transitions, the S{sub 1} → S{sub 0} internal conversion is major (55%) but the S{sub 1} → T{sub 1} intersystem crossing is still comparable and cannot be ignored, which accounts for 28%. Finally, we have found a radical channel generating the molecular products of CH{sub 2}CO and H{sub 2}S, which is complementary to the concerted molecular channel. The present work sets the stage for simulating photodissociation dynamics of similar thio-carbonyl systems in matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Tether Dynamics Simulation Workshop summary

The Tether Dynamics Simulation Workshop focused on the efforts of the Tether Applications Simulation Working Group (TASWG) to catalog various dynamics simulations, document environmental models, and provide a set of verified simulation results. The workshop consisted of reports on these activities and the presentation of papers on current dynamics topics of general interest. This paper documents the work performed at the Workshop and the results and recommendations for further work.

Rupp, Charles C.↗
DOE OSTI2015

Molecular dynamics simulations of large macromolecular complexes

Connecting dynamics to structural data from diverse experimental sources, molecular dynamics simulations permit the exploration of biological phenomena in unparalleled detail. Advances in simulations are moving the atomic resolution descriptions of biological systems into the million-to-billion atom regime, in which numerous cell functions reside. In this opinion, we review the progress, driven by large-scale molecular dynamics simulations, in the study of viruses, ribosomes, bioenergetic systems, and other diverse applications. Finally, these examples highlight the utility of molecular dynamics simulations in the critical task of relating atomic detail to the function of supramolecular complexes, a task that cannot be achieved by smaller-scale simulations or existing experimental approaches alone.

59 BASIC BIOLOGICAL SCIENCES↗