scholarly journals Molecular Dynamics Study of Hydrogen on Alkali-Earth Metal Cations Exchanged X Zeolites

2014 ◽  
Vol 2014 ◽  
pp. 1-9
Author(s):  
Du Xiaoming
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Knudsen Diffusion ◽  
Earth Metal ◽  
The Self ◽  
Pulse Field ◽  
Self Diffusion ◽  
Hydrogen Molecules ◽  
X Zeolites ◽  
Diffusion Of Hydrogen

The self-diffusion of hydrogen in Ca2+-, Mg2+- and Ba2+-exchanged X zeolites (Mg46X, Ca46X, and Ba46X) has been studied by molecular dynamics (MD) simulations for various temperatures and loadings. The results indicate that in the temperature range of 77–298 K and the loading range of 1–80 molecules/cell, the self-diffusion coefficients are found to range from1.2×10-9 m2·s−1to2.3×10-7 m2·s−1which are in good agreement with the experimental values from the quasielastic neutron scattering (QENS) and pulse field gradients nuclear magnetic resonance (PFG NMR) measurements. The self-diffusion coefficients decrease with loading due to packing of sorbate-sorbate molecules which causes frequent collusion among hydrogen molecules in pores and increases with increasing temperature because increasing the kinetic energy of the gas molecules enlarges the mean free path of gas molecule. The mechanism of diffusion of hydrogen molecules in these zeolites is transition diffusion. Knudsen diffusion occurs at low loading and the molecular bulk diffusion occurs at higher loading. For given temperature and loading, the self-diffusion coefficients decrease in the orderBa46X<Mg46X<Ca46X, due to the different sizes and locations of the divalent cations. Moreover, the effect of concentration of molecular hydrogen on self-diffusion coefficient also is analyzed using radial distribution function (RDF).

scholarly journals Molecular-Dynamics Simulation of Self-Diffusion of Molecular Hydrogen in X-Type Zeolite

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Xiaoming Du
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Hydrogen Diffusion ◽  
Mean Free Path ◽  
The Self ◽  
Dynamics Simulation ◽  
Pulse Field ◽  
Self Diffusion ◽  
Hydrogen Molecules ◽  
Dynamics Simulations

The self-diffusion of hydrogen in NaX zeolite has been studied by molecular-dynamics simulations for various temperatures and pressures. The results indicate that in the temperature range of 77–293 K and the pressure range of 10–2700 kPa, the self-diffusion coefficients are found to range from 1.61 × 10−9 m2·s−1to 3.66 × 10−8 m2·s−1which are in good agreement with the experimental values from the quasielastic neutron scattering (QENS) and pulse field gradients nuclear magnetic resonance (PFG NMR) measurements. The self-diffusion coefficients decrease with increasing pressure due to packing of sorbate-sorbate molecules which causes frequent collusion among hydrogen molecules in pores and increase with increasing temperature because increasing the kinetic energy of the gas molecules enlarges the mean free path of gas molecule. The activated energy for hydrogen diffusion determined from the simulation is pressure-dependent.

Molecular-Dynamics Analysis of the Structural Properties of Silica during Cooling

2008 ◽  
Vol 139 ◽  
pp. 101-106 ◽  
Author(s):  
Byoung Min Lee ◽  
Shinji Munetoh ◽  
Teruaki Motooka ◽  
Yeo Wan Yun ◽  
Kyu Mann Lee
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Transition Temperature ◽  
Structural Properties ◽  
Diffusion Coefficients ◽  
The Self ◽  
Dynamics Analysis ◽  
Self Diffusion ◽  
Dynamics Simulations ◽  
Potential Parameters

The structural properties of SiO2 liquid during cooling have been investigated by molecular dynamics simulations. The interatomic forces acting on the particles are calculated by the modified Tersoff potential parameters. The glass transition temperature and structural properties of the resulting SiO2 system at various temperatures have been investigated. The fivefold coordinations of Si and threefold coordinations of O atoms were observed, and the coordination defects of system decrease with decreasing temperature up to 17 % at 300 K. The self-diffusion coefficients for Si and O atoms drop to almost zero below 3000 K. The structures were distorted at high temperatures, but very stable atomic network persisted up to high temperature in the liquid state.

A Molecular Dynamics Simulation of Molten (Li-Rb)Cl Implying the Chemla Effect of Mobilities

1980 ◽  
Vol 35 (5) ◽  
pp. 493-499 ◽  
Author(s):  
Isao Okada ◽  
Ryuzo Takagi ◽  
Kazutaka Kawamura
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Diffusion Coefficients ◽  
Strong Correlation ◽  
Pair Correlation ◽  
The Self ◽  
Dynamics Simulation ◽  
Self Diffusion ◽  
Pure Salt ◽  
Dynamics Simulations

Abstract A new transport property, the self-exchange velocity (SEV) of neighbouring unlike ions, has been evaluated from molecular dynamics simulations of molten LiCl, RbCl and LiRbCl2 at 1100 K and the mixture at 750 K. From the increase of the SEV's in the order Rb+ (pure salt) <Li+ (mixture) < Rb+ (mixture) < Li+ (pure salt), it is conjectured that there is a strong correlation between the SEV’s and the internal mobilities. An interpretation of the Chemla effect in its dependence on temperature is given. The pair correlation functions and the self-diffusion coefficients are also calculated and discussed.

scholarly journals Diffusion of fructose in water: a molecular dynamics study

2020 ◽  
pp. 30-44
Author(s):  
Santosh Bhusal ◽  
Nurapati Pantha
Keyword(s):  
Molecular Dynamics ◽  
Mole Fraction ◽  
Diffusion Coefficients ◽  
Mean Square Displacement ◽  
The Self ◽  
Arrhenius Behavior ◽  
Binary Diffusion ◽  
Self Diffusion ◽  
Water Solvent ◽  
Binary Diffusion Coefficients

Present work carries the molecular dynamics (MD) simulation to study the self-diffusion coefficients of fructose (C6H12O6) and SPC/E (Extended Simple Point Charge) water (H2O) along with their binary diffusion coefficients at different temperature (298.15 K, 303.15 K, 308.15 K and 312.15 K). A dilute solution of 3 molecules of fructose (solute, mole fraction 0.0018) and 1624 molecules of water (solvent, mole fraction 0.9982) has been taken for making it relevant to the previously reported experiment. The structural analysis of the mixture has been estimated by using the radial distribution function (RDF) of its constituents. Mean square displacement (MSD) and Einstein’s relation have been used to find the self-diffusion coefficients of both the solute and solvent. Furthermore, Darken’s relation finds the binary diffusion coefficients. The temperature dependence of diffusion coefficients follows the Arrhenius behavior which further calculates activation energy of diffusion. The results from the present work agree well with the previously reported experimental values.

Computer Simulation of Diffusion of Pb-Bi Eutectic in Liquid Sodium by Molecular Dynamics Method

2002 ◽  
Author(s):  
Yingxia Qi ◽  
Minoru Takahashi
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Process ◽  
Diffusion Coefficients ◽  
The Self ◽  
Molecular Dynamics Method ◽  
Pure Liquid ◽  
Empirical Equations ◽  
Potential Candidate ◽  
Self Diffusion ◽  
Dynamics Method

Lead-bismuth eutectic is a potential candidate for coolant of secondary loops of sodium-cooled fast breeder reactors (FBR). The studies on the diffusion of liquid Pb-Bi in liquid Na are carried out corresponding to the case that liquid Pb-Bi leaks to liquid Na by accident. As the diffusion processes are the results of atomic motions, molecular dynamics method has been used to study the diffusion process. The self-diffusion coefficients of pure liquid Pb and Na, and liquid Pb-Bi are calculated and compared with ones by the empirical equations. The discrepancy between them could be eliminated by changing the densities of the liquids. The diffusion of lead-bismuth in sodium is simulated based on the changed densities under which the self-diffusion coefficients of individual liquid metals are close to those by the empirical equations. The simulation results show that the diffusion process of liquid Pb-Bi in liquid Na is a heat releasing process and the density of ternary liquid Na-Pb-Bi is higher than the average value of the densities of liquid Na and liquid Pb-Bi. It is also found that the diffusion coefficients of liquid Pb-Bi in liquid Na are much higher than their self-diffusion coefficients, indicating that liquid Pb-Bi are easy and quickly to diffuse in liquid Na. However, the diffusion coefficient of liquid Na is decreased due to the existence of liquid Pb-Bi, implying that liquid Na-Pb-Bi have a higher viscosity than that of pure liquid Na.

Transport coefficients of the Lennard–Jones fluid by molecular dynamics

1986 ◽  
Vol 64 (7) ◽  
pp. 773-781 ◽  
Author(s):  
D. M. Heyes
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Bulk Viscosity ◽  
Shear Viscosity ◽  
Diffusion Coefficients ◽  
Transport Coefficients ◽  
The Self ◽  
Nonequilibrium Molecular Dynamics ◽  
Self Diffusion ◽  
Lennard Jones

New nonequilibrium molecular dynamics (MD) calculations of the shear viscosity, bulk viscosity, and thermal conductivity are presented. Together with the self-diffusion coefficients obtained from equilibrium MD, the success of the Dymond–Batchinski expressions for the density and temperature dependence of these transport coefficients is demonstrated.The shear viscosity and self-diffusion coefficients are very good probes for the approach point of the solid-to-liquid phase change. The bulk viscosity and thermal conductivity are less useful in this respect.

Translational and rotational dynamics in supercritical methanol from molecular dynamics simulation

2004 ◽  
Vol 76 (1) ◽  
pp. 203-213 ◽  
Author(s):  
Michalis Chalaris ◽  
J. Samios
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Md Simulation ◽  
Time Correlation ◽  
The Self ◽  
Dynamics Simulation ◽  
Supercritical Methanol ◽  
Reorientational Motion ◽  
Self Diffusion ◽  
Theoretical Predictions

The purpose of this paper is to review our latest molecular dynamics (MD) simulation studies on the temperature and density dependence of the translational and reorientational motion in supercritical (SC) methanol. In the present treatment, Jorgensen's [W. L. Jorgensen. J. Phys. Chem. A102, 8641 (1998)] transferable potential model, tested in a recent MD study of hydrogen bonds in this fluid [M. Chalaris and J. Samios, J. Phys. Chem. B103, 1161 (1999)], was employed to simulate the dynamics of the system. The simulations were performed in the canonical (NVT) ensemble along the isotherms 523, 623, and 723 K and densities corresponding to the pressures from 10 to 30 MPa. Several dynamical properties of the fluid have been obtained and analyzed in terms of appropriate time-correlation functions (CFs). With respect to the translational dynamics, the self-diffusion coefficients obtained have been used to test the applicability of the well-known Chapman-Enskog kinetic theory. We have found that the theoretical predictions for the self-diffusion coefficients are only in qualitative agreement with the MD results over the whole temperature and density range studied. Finally, the inspection of the reorientational CFs and their corresponding correlation times lead to the conclusion that the reorientational motion of the SC methanol molecules in the sample is anisotropic.

scholarly journals A formation and growth model of CO2 hydrate layer based on molecular dynamics

2020 ◽  
Author(s):  
Kota Honda ◽  
Rintaro Fujikawa ◽  
Xiao MA ◽  
Norifumi Yamamoto ◽  
Kota Fujiwara ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Mass Transfer ◽  
Layer Thickness ◽  
Diffusion Coefficients ◽  
The Self ◽  
Dynamics Simulation ◽  
Dissolution Behavior ◽  
Transfer Coefficients ◽  
Hydrate Layer ◽  
Self Diffusion

This study develops a model to predict the CO2 hydrate layer thickness. As to achieve this, we need the mass transfer coefficients at the interface between water phase and CO2 hydrate layer and the diffusion coefficients in CO2 hydrate. Firstly, we conducted the visualization experiment of CO2 hydrate layer dissolution behavior. From the experiment, we obtain the mass transfer coefficient on the CO2 hydrate layer. The experimental results show good agreement with the existing empirical equation. Secondly, we conducted the molecular dynamics simulation of CO2 hydrate to obtain the self-diffusion coefficients of CO2 and H2O molecules. As to calculate the self-diffusion coefficients, we identified inter-cage hopping and intra-cage movement of molecules based on each molecule travel distance. Finally, the results indicate that the kinetic model we proposed reproduce the layer thickness on the order.

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