Multiscale Study of Gas Slip Flows in Nanochannels

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Quy Dong To ◽  
Thanh Tung Pham ◽  
Vincent Brites ◽  
Céline Léonard ◽  
Guy Lauriat
Keyword(s):  
Density Functional ◽  
Interaction Model ◽  
Maxwell Model ◽  
Theoretical Models ◽  
Md Simulations ◽  
Gas Flows ◽  
Simulation And Modeling ◽  
Slip Effects ◽  
Accommodation Coefficients ◽  
Ar Gas

A multiscale modeling of the anisotropic slip phenomenon for gas flows is presented in a tree-step approach: determination of the gas–wall potential, simulation and modeling of the gas–wall collisions, simulation and modeling of the anisotropic slip effects. The density functional theory (DFT) is used to examine the interaction between the Pt–Ar gas–wall couple. This potential is then passed into molecular dynamics (MD) simulations of beam scattering experiments in order to calculate accommodation coefficients. These coefficients enter in an effective gas–wall interaction model, which is the base of efficient MD simulations of gas flows between anisotropic surfaces. The slip effects are quantified numerically and compared with simplified theoretical models derived in this paper. The paper demonstrates that the DFT potential is in good agreement with empirical potentials and that an extension of the Maxwell model can describe anisotropic slip effects due to surface roughness, provided that two tangential accommodation parameters are introduced. MD data show excellent agreement with the tensorial slip theory, except at large Kundsen numbers (for example, Kn ≃0.2) and with an analytical expression which predicts the ratio between transverse and longitudinal slip velocity components.

Multiscale Study of Gas Slip Flows in Nanochannels

2013 ◽  
Author(s):  
Quy Dong To ◽  
Thanh Tung Pham ◽  
Vincent Brites ◽  
Céline Léonard ◽  
Guy Lauriat
Keyword(s):  
Density Functional ◽  
Effective Interaction ◽  
Theoretical Models ◽  
Md Simulations ◽  
Gas Flows ◽  
Multi Scale ◽  
Slip Effects ◽  
Accommodation Coefficients ◽  
Ar Gas ◽  
Slip Flows

In this paper, a multi-scale modeling of the anisotropic slip phenomenon for gas flows is presented. The analysis is carried out by using two principal computational methods: the Density Functional Theory and the Molecular Dynamics approach. The ab-initio method is used to examine the interaction between the Pt-Ar gas-wall couple, and to determine the effective potential. The potential is then implemented into a MD code in order to simulate beam scattering experiments and to calculate the accommodation coefficients. The results are used to model the effective interaction for isotropic or anisotropic surfaces. Further MD simulations, based on the effective gas-wall model for anisotropic surfaces, are conducted. The slip effects are quantified numerically and compared with simplified theoretical models, also derived in this paper.

Establishing a data-based scattering kernel model for gas–solid interaction by molecular dynamics simulation

2021 ◽  
Vol 928 ◽  
Author(s):  
Zijing Wang ◽  
Chengqian Song ◽  
Fenghua Qin ◽  
Xisheng Luo
Keyword(s):  
Machine Learning ◽  
Molecular Dynamics ◽  
Md Simulation ◽  
Rarefied Gas ◽  
Interaction Model ◽  
Md Simulations ◽  
Dynamics Simulation ◽  
Rarefied Gas Flows ◽  
Accommodation Coefficients ◽  
Scattering Kernel

Scattering kernel models for gas–solid interaction are crucial for rarefied gas flows and microscale flows. However, most existing models depend on certain accommodation coefficients (ACs). We propose here to construct a data-based model using molecular dynamics (MD) simulation and machine learning. The gas–solid interaction is first modelled by 100 000 MD simulations of a single gas molecule reflecting on the wall surface, which is fulfilled by GPU parallel technology. The results showed a correlation of the reflection velocity with the incidence velocity in the same direction, and also revealed correlations that may exist in different directions, which are neglected by the traditional gas–solid interaction model. Inspired by the sophisticated Cercignani–Lampis–Lord (CLL) model, two improved scattering kernels were constructed to better reproduce the probability density of velocity determined from MD simulation. The first one adopts variable ACs which depend on the incidence velocity and the second one combines three CLL-like kernels. All the parameters in the improved kernels are automatically chosen by the machine learning method. Compared with the numerical experiments of a molecular beam, the reconstructed scattering kernels are basically consistent with the MD results.

Computationally Assisted Design of High Signal-to-Noise Photoinduced Electron Transfer-Based Voltage-Sensitive Dyes

2020 ◽  
Author(s):  
Rishikesh Kulkarni ◽  
Anneliese Gest ◽  
Chun Kei Lam ◽  
Benjamin Raliski ◽  
Feroz James ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Dft Calculations ◽  
Photoinduced Electron Transfer ◽  
Density Functional ◽  
Embryonic Stem ◽  
High Sensitivity ◽  
Md Simulations ◽  
High Signal ◽  
Signal To Noise ◽  
Green Fluorescent

<p>High signal-to-noise optical voltage indicators will enable simultaneous interrogation of membrane potential in large ensembles of neurons. However, design principles for voltage sensors with high sensitivity and brightness remain elusive, limiting the applicability of voltage imaging. In this paper, we use molecular dynamics (MD) simulations and density functional theory (DFT) calculations to guide the design of a bright and sensitive green-fluorescent voltage-sensitive fluorophore, or VoltageFluor (VF dye), that uses photoinduced electron transfer (PeT) as a voltage-sensing mechanism. MD simulations predict an 11% increase in sensitivity due to membrane orientation, while DFT calculations predict an increase in fluorescence quantum yield, but a decrease in sensitivity due to a decrease in rate of PeT. We confirm these predictions by synthesizing a new VF dye and demonstrating that it displays the expected improvements by doubling the brightness and retaining similar sensitivity to prior VF dyes. Combining theoretical predictions and experimental validation has resulted in the synthesis of the highest signal-to-noise green VF dye to date. We use this new voltage indicator to monitor the electrophysiological maturation of human embryonic stem cell-derived medium spiny neurons. </p>

scholarly journals Measuring the structure and equation of state of polyethylene terephthalate at megabar pressures

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
J. Lütgert ◽  
J. Vorberger ◽  
N. J. Hartley ◽  
K. Voigt ◽  
M. Rödel ◽  
...  
Keyword(s):  
Equation Of State ◽  
Polyethylene Terephthalate ◽  
Density Functional ◽  
Equations Of State ◽  
Md Simulations ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
Shock Hugoniot ◽  
Highly Correlated

AbstractWe present structure and equation of state (EOS) measurements of biaxially orientated polyethylene terephthalate (PET, $$({\hbox {C}}_{10} {\hbox {H}}_8 {\hbox {O}}_4)_n$$ ( C 10 H 8 O 4 ) n , also called mylar) shock-compressed to ($$155 \pm 20$$ 155 ± 20 ) GPa and ($$6000 \pm 1000$$ 6000 ± 1000 ) K using in situ X-ray diffraction, Doppler velocimetry, and optical pyrometry. Comparing to density functional theory molecular dynamics (DFT-MD) simulations, we find a highly correlated liquid at conditions differing from predictions by some equations of state tables, which underlines the influence of complex chemical interactions in this regime. EOS calculations from ab initio DFT-MD simulations and shock Hugoniot measurements of density, pressure and temperature confirm the discrepancy to these tables and present an experimentally benchmarked correction to the description of PET as an exemplary material to represent the mixture of light elements at planetary interior conditions.

scholarly journals H2 Transformations on Graphene Supported Palladium Cluster: DFT-MD Simulations and NEB Calculations

Catalysts ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1306
Author(s):  
Francesco Ferrante ◽  
Antonio Prestianni ◽  
Marco Bertini ◽  
Dario Duca
Keyword(s):  
Atomic Hydrogen ◽  
Density Functional ◽  
Hydrogen Molecule ◽  
Md Simulations ◽  
Vacant Site ◽  
Functional Theory ◽  
H2 Adsorption ◽  
Palladium Cluster ◽  
Supported Palladium ◽  
Dynamics Simulations

Molecular dynamics simulations based on density functional theory were employed to investigate the fate of a hydrogen molecule shot with different kinetic energy toward a hydrogenated palladium cluster anchored on the vacant site of a defective graphene sheet. Hits resulting in H2 adsorption occur until the cluster is fully saturated. The influence of H content over Pd with respect to atomic hydrogen spillover onto graphene was investigated. Calculated energy barriers of ca. 1.6 eV for H-spillover suggest that the investigated Pd/graphene system is a good candidate for hydrogen storage.

A Modified Thermal Boundary Resistance Model for FCC Structures

2009 ◽  
Author(s):  
Ruijie Zhao ◽  
Yunfei Chen ◽  
Kedong Bi ◽  
Meihui Lin ◽  
Zan Wang
Keyword(s):  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Theoretical Calculations ◽  
Theoretical Models ◽  
Md Simulations ◽  
Boundary Resistance ◽  
Nonequilibrium Molecular Dynamics ◽  
Thermal Boundary Resistance ◽  
Inelastic Channel ◽  
The Right

A modified lattice-dynamical model is proposed to calculate the thermal boundary resistance at the interface between two fcc lattices. The nonequilibrium molecular dynamics (MD) simulation is employed to verify the theoretical calculations. In our physical model, solid crystal argon is set at the left side and the right side structure properties are tunable by setting the atomic mass and the interactive energy strength among atoms with different values. In the case of mass mismatch, the predictions of the lattice-dynamical (LD) model agree well at low temperature while the calculations of the diffuse mismatch model (DMM) based on the detailed phonon dispersion agree well at high temperature with the MD simulations. The modified LD model, considering a partially specular and partially diffuse phonon scattering, can explain the simulations reasonably in the whole temperature rage. The good agreement between the theoretical calculations and the simulations may be attributed to that phonon scattering mechanisms are dominated by elastic scattering at the perfect interfaces. In the case of interactive energy strength mismatch, the simulations are under the predictions of both the theoretical models, which may be attributed to the fact that this mismatch can bring about an outstanding contribution to opening up an inelastic channel for heat transfer at the interfaces.

Molecular Dynamic Structure Investigations of the Surface Stability and Adsorption of H, H2, CH3, C2H2: (100) Diamond

1992 ◽  
Vol 270 ◽  
Author(s):  
Th. Frauenheim ◽  
P. Blaudeck ◽  
D. Porezag
Keyword(s):  
Density Functional ◽  
Dynamic Structure ◽  
Md Simulations ◽  
Diamond Surface ◽  
Diamond Growth ◽  
Minimal Basis ◽  
Surface Stability ◽  
Hydrogen Supply ◽  
Reaction Processes ◽  
Structure Investigations

ABSTRACTSurface properties - stability and reconstruction - of clean and hydrogenated diamond (100) have been studied by real temperature molecular dynarnic (MD) simulations using an approximate density functional (DF) theory expanding the total electronic wave function in a minimal basis of localized atomic valence electron orbitals (LCAO - ansatz). The clean surface is highly unstable against a spontaneous dimerization resulting in a 2×1 reconstruction. Atomic hydrogen in the gas phase above the top surface at all temperatures and H2 molecules approaching the center of the dimer bond at room temperature are reactive in breaking the dimer π-bonds forming a monohydrogenated surface which maintains a stable 2×1 structure but with elongated surface C-C dimer bonds remaining stable against continuing hydrogen supply. The dihydrogenated surface taking a 1×1 structure, because of steric overcrowding dynamically becomes unstable against forming a 1×1 (alternating) di-, monohydrogenated surface. As first elementary reaction processes which may be discussed in relation to diamond growth we studied the thermal adsorption of CH3 and C2H2 onto a clean 2×l reconstructed (100) diamond surface.

Multiscale Simulations of Domains in Ferroelectrics

Domain Walls ◽  
2020 ◽  
pp. 311-339
Author(s):  
S. Liu ◽  
I. Grinberg ◽  
A. M. Rappe
Keyword(s):  
Density Functional ◽  
Large Scale ◽  
Mean Field Theory ◽  
Mean Field ◽  
Md Simulations ◽  
Relaxor Ferroelectrics ◽  
Ferroelectric Materials ◽  
Multiscale Simulations ◽  
Challenges And Opportunities ◽  
Physically Based

This chapter focuses on recent studies of ferroelectrics, where large-scale molecular dynamics (MD) simulations using first-principles-based force fields played a central role in revealing important physics inaccessible to direct density functional theory (DFT) calculations but critical for developing physically-based free energy functional for coarse-grained phase-field-type simulations. After reviewing typical atomistic potentials of ferroelectrics for MD simulations, the chapter describes a progressive theoretical framework that combines DFT, MD, and a mean-field theory. It then focuses on relaxor ferroelectrics. By examining the spatial and temporal polarization correlations in prototypical relaxor ferroelectrics with million-atom MD simulations and novel analysis techniques, this chapter shows that the widely accepted model of polar nanoregions embedded in a non-polar matrix is incorrect for Pb-based relaxors. Rather, the unusual properties of theses relaxor ferroelectrics stem from the presence of a multi-domain state with extremely small domain sizes (2–10 nanometers), giving rise to a greater flexibility for polarization rotations and the ultrahigh dielectric and piezoelectric responses. Finally, this chapter discusses the challenges and opportunities for multiscale simulations of ferroelectric materials.

scholarly journals The Influence of Gas–Wall and Gas–Gas Interactions on the Accommodation Coefficients for Rarefied Gases: A Molecular Dynamics Study

Micromachines ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 319 ◽  
Author(s):  
Shahin Mohammad Nejad ◽  
Silvia Nedea ◽  
Arjan Frijns ◽  
David Smeulders
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Rarefied Gas ◽  
Interaction Strength ◽  
Gold Surface ◽  
Md Simulations ◽  
Accommodation Coefficients ◽  
Experimental Values ◽  
Energy And Momentum ◽  
Gas Interactions

Molecular dynamics (MD) simulations are conducted to determine energy and momentum accommodation coefficients at the interface between rarefied gas and solid walls. The MD simulation setup consists of two parallel walls, and of inert gas confined between them. Different mixing rules, as well as existing ab-initio computations combined with interatomic Lennard-Jones potentials were employed in MD simulations to investigate the corresponding effects of gas-surface interaction strength on accommodation coefficients for Argon and Helium gases on a gold surface. Comparing the obtained MD results for accommodation coefficients with empirical and numerical values in the literature revealed that the interaction potential based on ab-initio calculations is the most reliable one for computing accommodation coefficients. Finally, it is shown that gas–gas interactions in the two parallel walls approach led to an enhancement in computed accommodation coefficients compared to the molecular beam approach. The values for the two parallel walls approach are also closer to the experimental values.

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