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  • 1
    Electronic Resource
    Electronic Resource
    Isothermal–isobaric molecular dynamics simulation of polymorphic phase transitions in alkali halides (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3148-3159 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: As the first application of the isothermal–isobaric molecular dynamics technique to a system with Coulombic forces, the pressure-induced face-centered-cubic to body-centered-cubic transition of some alkali halides is studied assuming Born–Mayer–Huggins potentials between the ions. The long-range forces are handled by the cubic harmonic expansion of the Ewald summation. The property that any periodic boundary condition of orthorhombic symmetry can be uniformly treated in this expansion allows the independent fluctuation of each box length in the course of the simulation of the isobaric ensemble. This reduces stresses during phase transitions from one crystalline state to another and yields less defects. By the appropriate change in the external pressure, the fcc–bcc transition takes place reversibly only in the presence of a considerable amount of defects. Otherwise, quite large hysteresis is found. It is shown that the [100], [010], and [001] directions of the original fcc lattice become the [ 1/2 1/2 1¯], [1¯01], and [111] directions in the bcc lattice, respectively. This confirms the Watanabe–Tokonami–Morimoto mechanism supported also by most of the experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456936
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  • 2
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics study of shear and shear-free flows in simple fluids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10217-10225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonequilibrium molecular dynamics simulations have been performed in order to compare the characteristics of planar Couette, planar elongation, uniaxial stretching, and biaxial stretching flows in simple fluids at different strain rates. After deriving the periodic boundary conditions for general flow fields and introducing some methodological improvements for elongation flow calculations we simulated the combination of shear and shear-free flows as well. We found that even at high strain rates where simple fluids exhibit strong non-Newtonian behavior (shear-thinning) it is a reasonable approximation to consider the two planar flows to be rotationally equivalent. This is because in planar Couette flow the in-plane normal stress difference of simple fluids is approximately zero even far from equilibrium. Similarly to planar Couette flow, the trace of the pressure tensor and the internal energy vary approximately as function of the 3/2 power of the strain rate in shear free flows. However, the individual diagonal elements of elongation flow pressure tensors deviate considerably from this approximation. In the extension direction the pressure seems to have a minimum in terms of the strain rate in every shear-free flow. We have discussed the implications of these results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469925
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of transport properties from molecular dynamics simulation (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5070-5075 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the self-diffusion as an example, we present a novel molecular dynamics method which fixes a transport property of the system to a prescribed value. We discuss the technical realization of the algorithm for this history dependent property. Owing to the monotonic temperature vs self-diffusion relationship for a given model substance at fixed density the system automatically chooses that temperature which corresponds to the input value of the self-diffusion coefficient. In principle, this approach can be applied to other transport coefficients too. In practice, however, the numerical calculation of transport properties expressed by the collective dynamics of particles is very time consuming from equilibrium molecular dynamics simulation. Our method being an equivalent of the Green–Kubo integral also performs poorly compared to nonequilibrium molecular dynamics techniques. We present details and results of model calculations for these two transport processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467363
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  • 4
    Electronic Resource
    Electronic Resource
    Towards the atomistic simulation of phase coexistence in nonequilibrium systems (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2378-2390 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical approach is presented which represents the first attempt known to the authors to develop molecular dynamics algorithms capable of modeling phase coexistence between two nonequilibrium steady state phases confined in a closed (E,V,N) system. We deal exclusively with shearing liquids because of their importance in rheology. In the present paper, as in the equilibrium Gibbs ensemble Monte Carlo technique for systems at equilibrium, the coexisting phases have no physical contact but their dynamics are coupled in order to reach mechanical, thermal, and composition balance between bulk regions of the two phases. The thermal balance is maintained by requiring zero net heat flow across a hypothetical boundary. This can be achieved by starting from equilibrium and gradually increasing the strength of the external field (the shear rate) in a quasistatic process. For particle interchanges we invoke the Evans–Baranyai variational principle which is at the very least a good approximation for similar simulated steady state systems far from equilibrium. Results of several model calculations are presented. The limitations and the implications of the methods are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472105
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  • 5
    Electronic Resource
    Electronic Resource
    Phase space compression and entropy of nonequilibrium steady states (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7723-7726 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that the variational principle of Evans and Baranyai (Phys. Rev. Lett. 67, 2597 (1991)] can be derived from a macroscopic entropy definition of nonequilibrium steady states. This definition claims that the entropy of nonequilibrium steady states is the sum of the equilibrium entropy of the system under the same external conditions (fixed internal energy, E, volume, V, and number of particles N), and an additional term which can be measured by the minimum excess work performed on the system by the external field, Fe, by bringing it from its equilibrium state to the final steady state. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472555
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  • 6
    Electronic Resource
    Electronic Resource
    On the configurational temperature of simple fluids (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3964-3966 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the formalism of liquid-state statistical mechanics, we study the properties of the recently derived configurational temperature [H. H. Rough, Phys. Rev. Lett. 78, 772 (1997)]. We show that the configurational temperature expression derived in the microcanonical ensemble is valid for open equilibrium systems as well. We also present a special way of deriving the configurational temperature for dilute gases. The same approach connects the pair-correlation function and the pair potential in the form of a sum rule which can be utilized in the integral equation theory of liquids. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480995
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  • 7
    Electronic Resource
    Electronic Resource
    Liquid–vapor coexistence by molecular dynamics simulation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3516-3522 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a simple and consistent molecular dynamics algorithm for determining the equilibrium properties of a bulk liquid and its coexisting vapor phase. The simulation follows the dynamics of the two systems simultaneously while maintaining the volume and the number of particles of the composite system fixed. The thermostat can constrain either the total energy or the temperature at a desired value. Division of the extensive properties between the two phases is governed by the difference of the corresponding intensive state variables. Particle numbers are continuous variables and vary only in virtual sense, i.e., the real sizes of the two systems are the same and do not change during the course of the simulation. Calculation of the chemical potential is separate from the dynamics; thus, one can replace the particle exchange step with other method if it improves the efficiency of the code. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480506
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  • 8
    Electronic Resource
    Electronic Resource
    Comment on "A new algorithm for reverse Monte Carlo simulations" [J. Chem. Phys. 109, 2624 (1998)] (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5620-5621 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The purpose of the reverse Monte Carlo method is to help in processing experimental data obtained from x-ray or neutron diffraction measurements and setup three-dimensional models plausible with chemical evidence and the results of the measurement. Although the "inverse theorem" provides certain theoretical footage to the method, it says nothing about the correct numerical details of the RMC algorithm. Unfortunately, the latter quality opens up opportunity for methodological studies with results of questionable values. Thus, we felt obliged to point to the problematic features of the paper of da Silva et al. [J. Chem. Phys. 109, 2624 (1998)] with the aim to draw the attention of the entire scientific community dealing with structural modeling. The debate can be very useful in clarifying the problematic details of the frequently criticized reverse Monte Carlo technique. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479826
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  • 9
    Electronic Resource
    Electronic Resource
    Steady state simulation of planar elongation flow by nonequilibrium molecular dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 42-45 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a novel method for performing steady state nonequilibrium molecular dynamics simulation of planar elongation flow based on the studies of Kraynik and Reinelt [Int. J. Multiphase Flow 18, 1045 (1992)]. These authors identified the orientation of the unit cell which leads to periodic behavior of the square lattice with the minimum period. This way the exponential deformation of the system periodically returns to a state where replacing some of the original particles with their images the initial state boundaries are recovered. We adopted their theoretical results to nonequilibrium molecular dynamics simulations and performed representative calculations for simple fluids. The new method solves the long-standing problem of simulating planar elongation flow in the steady state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478082
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  • 10
    Electronic Resource
    Electronic Resource
    Fluctuation of the pair-correlation function (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8575-8576 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a simple thermodynamic argument we derive an expression providing the r-dependent fluctuations of the pair-correlation function, g(r), of a liquid. The variance of g(r) at r is a function only of its own value at this point. Fluctuations calculated from Monte Carlo simulations fit well to this formula. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475009
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