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  • 11
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5464-5476 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Equilbrium properties of a rare-gas fluid contained between two parallel fcc(100) planes of rigidly fixed rare-gas atoms were computed by means of the grand-canonical ensemble Monte Carlo method. The singlet distribution function ρ(1), and the pair-correlation function g(2) in planes parallel to the solid layers, indicate that the structure of the pore fluid depends strongly on the distance h between the solid layers. As the separation increases from less than two atomic diameters, successive layers of fluid appear. The transitions between one and two layers and three and four layers are especially abrupt and are accompanied by changes in the character of g(2) from dense fluid-like to solid-like. Long-range, in-plane order in the fluid layers diminishes with increasing h, but is still evident in the contact layer (i.e., that nearest the solid layer) at h=16.5 atomic diameters, the largest separation considered. The structure of the contact layer reflects the solid-layer structure and differs significantly from the adjacent inner fluid layers, whose g(2) resembles that of the corresponding bulk fluid. Decreasing the density of atoms in the solid layers blunts the peaks in ρ(1) and g(2), although even for the least dense layer considered the contact layers of fluid evince long-range, in-plane order. Replacing the discrete pairwise fluid–solid interactions with the mean field resulting from smearing the solid atoms over the plane of the solid layer destroys the "phase transitions'' and the associated long-range, in-plane order.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 3584-3589 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider the classical motion of a harmonic lattice in which only those atoms in a certain subset of the lattice (primary zone) may interact with an external force. The formally exact generalized Langevin equation (GLE) for the primary zone is an appropriate description of the dynamics. We examine a previously proposed Brownian, or frictional damping, approximation that reduces the GLE to a set of coupled ordinary Langevin equations for the primary atoms. It is shown that the solution of these equations can contain undamped motion if there is more than one atom in the primary zone. Such motion is explicitly demonstrated for a model that has been used to describe energy transfer in atom–surface collisions. The inability of the standard Brownian approximation to yield an acceptable, physically meaningful result for primary zones comprising more than one atom suggests that the Brownian approximation may introduce other spurious dynamical effects. Further work on damping of correlated motion in lattices is needed.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3130-3137 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The "hemiquantal'' equations (HQE), which pertain to a system consisting of a quantally-behaving ("light'') subsystem coupled to a classically-behaving ("heavy'') one, result from a partial classical limit of Heisenberg's equations of motion. In effect, all heavy particles are required to follow precisely their classical trajectories. The HQE are applied to vibrational predissociation in a collinear model of the van der Waals molecule He ⋅ ⋅ ⋅I2(B). Here, the vibration of I2 is the classical subsystem and the motion of He relative to the center of mass of I2 is the quantal subsystem. In this case, the HQE comprise a partial differential equation (Schrödinger's equation for the He motion) coupled to two ordinary differential equations (Hamilton's equations for the I2 vibration). These were solved numerically on the CYBER 205 supercomputer by means of an algorithm that uses a second-order predictor–corrector for Hamilton's equations and second-order time differencing for Schrödinger's equation. A scheme based on the fast Fourier transform was used to evaluate the spatial derivative of the wave function. The computed rates of vibrational predissociation are compared with the results of previous quasiclassical and fully quantal calculations and with experimental results.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 3411-3424 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular description of friction at a single, ideal microscopic contact of the sort realizable in scanning surface probe devices is greatly complicated by wide variations in the temporal regime t*≡texpt/tr of the measurement, where texpt is the time taken to measure the frictional force Fs and tr is the time required for the system to attain a state of thermodynamic equilibrium. At one extreme (t*(very-much-greater-than)1) the system remains in equilibrium for the duration of the measurement and one can employ statistical thermodynamics (in practice, Monte Carlo simulation) to compute Fs, which depends only on the thermodynamic state. At the other extreme (t*(very-much-less-than)1) the system remains out of equilibrium. One must then account for the dynamic history of the system, typically by means of nonequilibrium molecular dynamics. The range of t* between these extremes can be handled within a single theoretical framework based on the concept of "equivalent equilibrated states." Through addition of auxiliary potential fields to the Hamiltonian specific degrees of freedom of the system can be constrained. The properties of the constrained system are computed from the free energy of the system trapped in the equivalent equilibrated state by the constraints. The constraints are chosen to correspond to t*. The results of the theory applied to a one-dimensional model demonstrate dramatically the impact of history on Fs. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 330 (1987), S. 461-463 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In our model each wall consists of a square 'unit cell' of the (100) plane of a face-centred-cubic (f.c.c.) lattice (Fig. 1). One wall lies in the z = 0 plane and the other in the z = h plane. The walls are positioned in the x- and ^-direction so that they are either adjacent (out of registry, as ...
    Type of Medium: Electronic Resource
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