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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4256-4260 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the Green–Bogoliubov method, we derive an expression for the thermodynamic pressure or grand potential density for a molecular model of a fluid confined in a disordered porous matrix. The expression is equivalent to the virial equation derived previously via the replica method [Rosinberg et al., J. Chem. Phys. 100, 5172 (1994)] but differs from an expression recently derived from the condition of mechanical equilibrium. It is concluded that the condition of mechanical equilibrium does not yield information about the thermodynamics of these systems. The thermodynamic pressure can be obtained from experiment indirectly by integrating the Gibbs adsorption isotherm and, in principle, by direct measurement. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9222-9239 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a density-functional theory of nonuniform fluids composed of polyatomic species. It is derived from Wertheim's first-order perturbation theory of polymerization by taking the limit of complete association. In the case of the uniform fluid, an explicit expression of the complete angle-dependent pair distribution function is obtained which shows that the theory yields nontrivial results for the intermolecular structure. However, features of the long-wavelength structure, such as the existence of an orientational order, are not described. Illustrative applications of the theory are given in the case of diatomic and linear tetra-atomic molecules formed by tangent hard spheres of the same diameter.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 11289-11298 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the phase diagram and the structure of a fluid adsorbed in high-porosity aerogels by means of an integral-equation approach combined with the replica formalism. To simulate a realistic gel environment, we use an aerogel structure factor obtained from an off-lattice diffusion-limited cluster–cluster aggregation process. The predictions of the theory are in qualitative agreement with the experimental results, showing a substantial narrowing of the gas–liquid coexistence curve (compared to that of the bulk fluid), associated with weak changes in the critical density and temperature. The influence of the aerogel structure (nontrivial short-range correlations due to connectedness, long-range fractal behavior of the silica strands) is shown to be important at low fluid densities. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9613
    Keywords: disordered systems ; spin glasses ; Ornstein–Zernike equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We propose a self-consistent Ornstein–Zernike approximation for studying the Edwards–Anderson spin glass model. By performing two Legendre transforms in replica space, we introduce a Gibbs free energy depending on both the magnetizations and the overlap order parameters. The correlation functions and the thermodynamics are then obtained from the solution of a set of coupled partial differential equations. The approximation becomes exact in the limit of infinite dimension and it provides a potential route for studying the stability of the high-temperature phase against replica-symmetry breaking fluctuations in finite dimensions. As a first step, we present the predictions for the freezing temperature T f and for the zero-field thermodynamic properties and correlation length above T f as a function of dimensionality.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9613
    Keywords: Solvable models ; one-dimensional systems ; density functional ; chemical association
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two models of one-dimensional fluids of associating hard rods in an arbitrary external field are investigated. In the first model particles can only form dimers, while in the second model, which has been solved previously by Percus, aggregates of any size coexist. In both cases the grand canonical potential and the external potential are found exactly as functionals of the density. It is shown that Wertheim's thermodynamic perturbation theory of polymerization provides a straightforward route to the exact solution by expanding the functional space to include more density parameters. This suggests that Wertheim's theory should be used also for studying the structure (and not only the thermo-dynamics) of real associating fluids.
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  • 7
    ISSN: 1572-9613
    Keywords: disordered systems ; Ornstein–Zernike equations ; random field Ising model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We extend the self-consistent Ornstein–Zernike approximation (SCOZA), first formulated in the context of liquid-state theory, to the study of the random field Ising model. Within the replica formalism, we treat the quenched random field just as another spin variable, thereby avoiding the usual average over the random field distribution. This allows us to study the influence of the distribution on the phase diagram in finite dimensions. The thermodynamics and the correlation functions are obtained as solutions of a set a coupled partial differential equations with magnetization, temperature, and disorder strength as independent variables. A preliminary analysis based on high-temperature and 1/d series expansions shows that the theory can predict accurately the dependence of the critical temperature on disorder strength (no sharp transition, however, occurs for d≤4). For the bimodal distribution, we find a tricritical point which moves to weaker fields as the dimension is reduced. For the Gaussian distribution, a tricritical point may appear for d around 4.
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model fluid composed of semiflexible tangent hard sphere trimers is investigated using Monte Carlo simulations and perturbation density functional theory (PDFT), focusing on the density profile and conformational properties in the vicinity of a hard wall. The surface density is reduced (enhanced) at low (high) densities. We also observe preferential end absorption. Both features arise from competition between chain conformational entropy and packing constraints. Molecules adjacent to the wall tend to lie flat against it, particularly at high density and/or stiffness. But the bond angle distribution is only weakly affected by the presence of the wall. For rigid molecules, the density profiles depend strongly on the value of the bond angle. PDFT is in excellent agreement with simulation, and promises to be a successful means of elucidating the interfacial structure of complex fluids. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7997-8003 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An equation of state for a fluid of fused hard sphere (FHS) molecules is developed based on an interpolation scheme which relates the free energy per particle to that of a fluid of tangent hard sphere (THS) molecules at the same packing fraction. Use of Wertheim's TPT1 (first order thermodynamic perturbation theory) equation for this latter quantity yields an analytical expression for the compressibility factor for any shape of the FHS molecule. Predictions are in good agreement with the simulation results for rigid homonuclear and heteronuclear diatomics, linear and nonlinear triatomics, and tetrahedral pentatomics. For purely repulsive models of n-alkane chains, it is found that the accuracy of the theory deteriorates with increasing chain length. The interpolation procedure is also generalized to the case of chemical association.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5326-5335 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Equations of state for hard sphere chain molecules are derived within the framework of second order perturbation theory of polymerization (TPT2). The present formulation differs from the original Wertheim's treatment by dealing with molecules with a fixed number of beads. However, the two versions yield very close numerical results for chains composed of freely jointed spheres, showing the insensitivity of the pressure of these fluids to polydispersity. The case of star-like molecules and chain mixtures is also considered. Theoretical predictions are compared to available simulation data, using recent results for the triplet correlation function for hard spheres in rolling contact. Some predictions for the pressure of freely rotating chains and that of trimers as a function of the bond angle are given.
    Type of Medium: Electronic Resource
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