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  • 1
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics calculation of self-diffusion in a non-Newtonian fluid subject to a Couette strain field (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2149-2158 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been performed on a simple fluid in the non-Newtonian regime in order to study the nature of diffusion in the presence of shear stress. The nonequilibrium molecular dynamics (NEMD) sllod algorithm is used to generate a homogeneous boundary driven Couette flow. The elements of the tensor of diffusion coefficients have been evaluated by three different routes: through Einstein relations with the corresponding elements of the tensor of molecule displacements, through Green–Kubo expressions involving tensor of momentum autocorrelation functions and cross-correlation functions, and by utilizing an NEMD color field method. All three routes to the tensor of diffusion coefficients are shown to yield consistent results. A simple spherically symmetric Lennard-Jones fluid at its triple point was used in the simulation study. We find that in a Couette strain field of sufficiently large strain rate, diffusion in all directions is enhanced substantially. We propose and verify a new asymptotic relationship between the diagonal elements of the tensor of diffusion coefficients and the strain rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459886
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic transition moment variation and Einstein coefficients for the NO(B 2Π–X 2Π) system (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7667-7676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper details an investigation of the variation in the electronic transition moment with internuclear separation for the NO(B2Π–X2Π) transition. Measurements of the relative intensities of a number of NO B–X vibronic transitions having a common upper level were used to construct a relative transition-moment function between 1.27 and 1.60 A(ring). After normalizing this relative function by experimentally determined radiative lifetimes, the transition-moment function was extended down to 1.23 A(ring) by incorporating data from oscillator strength measurements. In contrast to empirical transition-moment functions that have been proposed previously, the function in this paper decreases with increasing internuclear separation. Unlike these other functions, however, this one is consistent with theoretical predictions, with most available oscillator strength data, and with the observed trend in B-state radiative lifetimes as a function of vibrational level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460722
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  • 3
    Electronic Resource
    Electronic Resource
    A general solution of the molecular Ornstein–Zernike equation for spheres with anisotropic adhesion and electric multipoles (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3741-3747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the analytic solution of the molecular Ornstein–Zernike equation for a very general closure in which the direct correlation function is of the form suggested by the mean-spherical approximation for arbitrary multipolar interactions and the total correlation function contains terms that arise in the Percus–Yevick approximation for spheres with anisotropic surface adhesion. In addition to generalizing several earlier analyses of special cases of this closure, the solution presented here contains new simplifying insights that reduce the complexity of the resulting algebraic equations. A special case of the analysis is described to illustrate the method of solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457832
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular simulation of water along the liquid–vapor coexistence curve from 25 °C to the critical point (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7355-7359 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Previous work has shown that the simple point-charge (SPC) model can represent the experimental dielectric constant of water. In this work, we present results of Monte Carlo simulations of SPC water in the isothermal–isobaric (NPT) ensemble and in the Gibbs ensemble. Long-range intermolecular interactions are included in these simulations by use of the Ewald summation method. When Ewald sums are used, simulated, uniphase liquid potential energies are slightly lower (in absolute value) than those obtained for a simple spherical cutoff of the intermolecular potential. The coexistence curve of SPC water is obtained from 25 to 300°C. The critical constants of SPC water are estimated by adjusting the coefficients of a Wegner expansion to fit the difference between simulated liquid and vapor orthobaric densities; the estimated critical temperature is 314 °C and the estimated critical density is 0.27 g/cm3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459409
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  • 5
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics calculation of the shear viscosity of liquid water (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6391-6398 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The shear viscosity, pressure, and configurational (SPC) internal energy of liquid water at four densities along the 303.15 K isotherm are calculated using nonequilibrium molecular dynamics. The interaction between the water molecules is modeled by the SPC pair potential of Berendsen and co-workers. The simulation results are compared with experimental data at the same temperatures and densities. The shear viscosity is found to be approximately 50% lower than the experimental results but has a similar slope as a function of density. The results for the full SPC potential are compared to those of a model fluid whose pair potential is obtained by setting the electrostatic part of the SPC interaction to zero. The results for the shear viscosity are remarkably similar to those of SPC water, suggesting that the electrostatic interactions make a very small contribution to the viscosity for this fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455407
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  • 6
    Electronic Resource
    Electronic Resource
    A model for association in electrolytes. Analytic solution of the hypernetted-chain/mean spherical approximation (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 317-325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the structural and thermodynamic properties of electrolytes in which the association between oppositely charged ions (A++B−(arrow-right-and-left)AB) is represented by a sticky electrolyte model (SEM) which allows positive and negative ions of diameter σ to be bonded at a distance L≤σ/2. The model is solved for a 2–2 electrolyte at concentrations up to 2 M and for L=σ/2 using the hypernetted-chain (HNC) approximation for the correlation functions within the spherical core and the mean spherical (MS) approximation outside. The number of AB dimers at a separation L is found to increase with concentration while there is a reduction in the number of contact ion pairs below that predicted by the restricted primitive model (RPM) from which stickiness is absent. The structural and thermodynamic properties of the SEM and RPM prove to be significantly different and sufficiently interesting to justify future applications of the SEM to molten salts and molecular solvents, especially if the ion–ion interactions can be treated with greater accuracy. The equilibrium properties of the fully associated system of extended dipoles with charges separated at a distance L=σ/2 are also given in the mean spherical approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449772
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  • 7
    Electronic Resource
    Electronic Resource
    Solution of the Ornstein–Zernike equation in the vicinity of the critical point of a simple fluid (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4303-4311 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a comparison of the results obtained from numerical and analytical solutions of the mean spherical approximation for hard spheres with a Yukawa tail. The emphasis is on the location of the liquid–vapor critical point and the calculation of the associated critical exponents. This comparison allows us to draw some general conclusions concerning the accuracy of numerical solutions of the Ornstein–Zernike equation in the critical region. One important conclusion is that for any closure correctly describing the divergence of the isothermal compressibility along the critical isotherm, extremely accurate numerical work will be required to calculate the value of the exponent delta. We have also compared numerical solutions obtained inside the two phase region with those from the analytical continuation of the analytical solutions into this regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448820
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of three-body forces on the shear viscosity of liquid argon (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6206-6209 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present nonequilibrium molecular dynamics simulations of pure argon at a temperature of 135 K and density of 1.034 gm/cc using the highly accurate Barker–Fisher–Watts (BFW) model for the intermolecular potential. We consider the BFW potential both with and without the Axilrod–Teller three-body interaction. We find that the three-body potential has a very small effect on the shear viscosity: The predicted value in the presence of three-body forces is 3% less than that obtained without three-body forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468402
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of the rheological and dynamical properties of a model alkane fluid under confinement (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1273-1280 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the effect of wall–fluid interactions on the state conditions and the effective properties of a model dodecane fluid confined between parallel solid walls. A significant increase in the effective density of the confined fluid is observed with increasing strength of the wall–fluid interaction. The effect of the wall–fluid interaction on the rotational relaxation and diffusional relaxation of the fluid is seen in the significant slowing down of the relaxation with increasing wall–fluid interaction strength. The difference between the confined fluid and the three-dimensional bulk fluid is demonstrated by the strong anisotropy of the dynamical properties, the molecular rotation, and self-diffusion. The viscosity of the confined fluid shows a large difference between weak and strong wall–fluid interactions, and a significant difference from bulk fluid at low shear rate. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479312
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  • 10
    Electronic Resource
    Electronic Resource
    Computer simulation of dipolar fluids. Dependence of the dielectric constant on system size: A comparative study of Ewald sum and reaction field approaches (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1502-1504 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report Monte Carlo calculations on a Stockmayer fluid ( μ*=1, T*=1, ρ*=0.8) using both Ewald sum (EW) and reaction field (RF) approaches. We investigate the dependence of dielectric constant on system size. This dependence is less marked for EW than for RF. However, for a given number of particles the RF run time is substantially shorter. Both methods therefore offer some computational advantage. Overall, RF is to be preferred because of greater ease of programming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451189
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