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  • 1
    Electronic Resource
    Electronic Resource
    Rheology of n-alkanes by nonequilibrium molecular dynamics (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4555-4570 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have simulated sheared liquid n-butane and n-decane by isothermal nonequilibrium molecular dynamics. Both alkanes exhibit nonlinear rheological behavior. Shear thinning at small shear rates, second Newtonian viscosities at moderate shear rates, normal stresses, dilatancy, and birefringence are observed for both fluids. Zero shear rate viscosities were calculated for both fluids: η(γ=0)=0.24 cp for butane at T=292 K, η(γ=0)=0.159 cp for decane at 481 K. These viscosities agree with experimental data for both fluids. The zero shear rate butane viscosity agrees with the Green–Kubo result of Marechal and Ryckaert, Chem. Phys. Lett. 101, 548 (1983). Shear induced molecular rotation, deformation, and alignment are quantitatively described to give a complete picture of molecular behavior in a sheared fluid. Equilibrium and shear simulations of butane with modified dihedral potentials were performed to investigate the effect of molecular conformation on the rheological properties of butane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452731
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  • 2
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics study of shear flow in soft disks (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4760-4766 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonequilibrium molecular dynamics calculations of homogeneous shear flow in two dimensions have been performed on soft disks close to the freezing transition. Simulations at discrete shear rates, γ(overdot), reveal complex phase changes and dynamical behavior during extensive shear thinning and a difference in the values of the diagonal components of the pressure tensor. A shear thickening regime was also found near to γ(overdot)=10 but it had disappeared at γ(overdot)=50, in line with recent work by Woodcock. The calculations reveal that there is a change from an amorphous liquid structure at γ(overdot)=1.0 to a fluid microscopically layered along the stream lines at γ(overdot)=10 and higher shear rates. An intermediate two-phase region was observed at γ(overdot)=5 in which both amorphous and ordered phases coexist within the MD cell, containing 896 disks. In the ordered phase the particle dynamics are dominated by the imposed shear flow and can be reproduced in large part by simple models which exclude thermal motion. The time correlation functions are highly oscillatory which reflect well defined motion on a local distance scale. The soft disks spend most of their time trapped between similar disks in adjacent layers, in between rapid periods of "free-flight''. Instantaneous pictures of the high shear rate (γ(overdot)(approximately-greater-than)10) structure consequently show the presence of oscillating transitory strings of highly overlapping soft disks formed roughly perpendicular to those stably formed along the streamlines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449001
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Constrained molecular dynamics: Simulations of liquid alkanes with a new algorithm (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6933-6939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new algorithm for molecular dynamics simulation involving holonomic constraints. Constrained equations of motion are derived using Gauss' principle of least constraint. The algorithm uses a fast, exact solution for constraint forces and a new procedure to correct for accumulating numerical errors. We report several simulations of liquid n-butane and n-decane performed with the new algorithm. We obtain an average trans population of 60.6±1.5% in liquid butane at T=291 K and ρ=0.583 g/ml. This result essentially agrees with that from an earlier simulation by Ryckaert and Bellemans [Discuss. Faraday Soc. 66, 95 (1978)]. However, our simulations are substantially more precise; our run lengths are typically ∼20 times longer than those of Ryckaert and Bellemans. Our result also agrees with that from a recent simulation by Wielopolski and Smith (following paper). Thermodynamic and structural data from our simulations also agree well with results from the simulations discussed in the above articles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450613
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation functions for diatomic symmetric molecules from the RISM equation (1981)
    Springer
    Journal of statistical physics 24 (1981), S. 607-616 
    Details
    ISSN: 1572-9613
    Keywords: RISM equation ; diatomic ; correlation functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the solution of the RISM equation for diatomic symmetric molecules outlined in a previous paper, the site-site radial distribution function (RDF) is calculated and compared with the Monte Carlo results and the numerical RDF of Lowden and Chandler. The RDF calculated here and the numerical RDF of Lowden and Chandler agree well at intermediate and high densities. At low density, however, both have systematic errors. The agreement between the RDF calculated here and the Monte Carlo results suggests that a simplified formulation of the RISM solution may serve well as a reference system in a perturbation theory for diatomic fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01011378
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    Paper (German National Licenses)
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