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  • 1
    Electronic Resource
    Electronic Resource
    Capillary Waves at the Liquid-Vapor Interface. Widom-Rowlinson Model at Low Temperature (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 2807-2816 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100009a042
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  • 2
    Electronic Resource
    Electronic Resource
    Resolving vibrational and structural contributions to isothermal compressibility (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3983-3988 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The well-known and general "compressibility theorem" for pure substances relates κT =−(∂ ln V/∂p)N,T to a spatial integral involving the pair correlation function g(2). The isochoric inherent structure formalism for condensed phases separates g(2) into two fundamentally distinct contributions: a generally anharmonic vibrational part, and a structural relaxation part. Only the former determines κT for low-temperature crystals, but both operate in the liquid phase. As a supercooled liquid passes downward in temperature through a glass transition, the structural contribution to κT switches off to produce the experimentally familiar drop in this quantity. The Kirkwood–Buff solution theory forms the starting point for extension to mixtures, with electroneutrality conditions creating simplifications in the case of ionic systems. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476997
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  • 3
    Electronic Resource
    Electronic Resource
    Møller–Plesset convergence issues in computational quantum chemistry (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9711-9715 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Hartree–Fock self-consistent-field approximation has provided an invaluable conceptual framework and a standard computational procedure for atomic and molecular quantum theory. Its shortcomings are significant however, and require remediation. Møller–Plesset perturbation theory offers a popular correction strategy: it formally expands eigenfunctions and eigenvalues as power series in a coupling parameter λ that switches the Hamiltonian continuously between the Hartree–Fock form (λ=0) and the electron-correlating "physical" Hamiltonian (λ=1). Recent high-order Møller–Plesset numerical expansions indicate that the series can either converge or diverge at λ=1 depending on the chemical system under study. The present paper suggests at least for atoms that series convergence is controlled by the position of a singularity on the negative real λ axis that arises from a collective all-electron dissociation phenomenon. Nonlinear variational calculations for the two-electron-atom ground state illustrate this proposition, and show that series convergence depends strongly on oxidation state (least favorable for anions, better for neutrals, better yet for cations). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481608
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  • 4
    Electronic Resource
    Electronic Resource
    Test of closure approximations in equilibrium classical many-body theory (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7791-7798 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Many integral equations for numerically predicting pair correlation functions g(2) in classical fluids have been proposed, each based on its own "closure approximation.'' We have investigated a procedure for evaluating such closures, particularly their capacity to describe clustering under the influence of attractive interparticle forces. Our approach utilizes the Gaussian core model in a large closed system which, under sign change of the coupling constant λ, undergoes a collapse to form a single compact aggregate with known properties. In the infinite system limit this phenomenon causes inverse temperature (β) expansions, such as that for g(2), to diverge. By contrast available closures lead to convergent expansions for the Gaussian core model, but with a "critical point'' on the negative real βλ axis. Specific calculations have been performed illustrating this behavior for the BGYK and the PY integral equations. We suggest that the proximity of the artifactual negative-axis critical point to the origin (where the collapse singularity should actually appear) provides a measure of accuracy of closure approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454743
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  • 5
    Electronic Resource
    Electronic Resource
    Removing chemical bonding ambiguities in condensed media by steepest-descent quenching (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3252-3253 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Chemical bonds between neighboring pairs of atoms tend to be significantly shorter than distances between nonbonded pairs that are in "van der Waals'' contact. Consequently there is usually no theoretical uncertainty in identifying chemical bonds in cold dense media from the atomic pair correlation functions: covalently bonded pairs appear as isolated narrow peaks at small separation. Under elevated temperature and pressure conditions, however, this peak isolation disappears, leading to considerable apparent bonding ambiguity. Using molecular dynamics simulation for sulfur as a testing device, we show that removal of thermal distortion even in extremely hot and dense media by steepest-descent quenching on the potential energy hypersurface completely restores peak isolation and removes bonding ambiguity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453717
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  • 6
    Electronic Resource
    Electronic Resource
    Inherent structure theory of liquids in the hard-sphere limit (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4767-4775 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Atomic pair correlation functions for liquids provide an image of temperature-dependent short-range order. If the thermal ensemble of atomic configurations is mapped (by steepest descent on the potential hypersurface) onto potential energy minima, the pair correlation function from the resulting transformed configurations exhibits substantial image enhancement, revealing short-range order in a much more vivid fashion. Previous studies of model atomic liquids have demonstrated that at fixed density, mapped short-range order is virtually independent of the initial temperature, and thereby amounts to an "inherent structure'' for the liquid. The present paper investigates steepest-descent mapping and inherent structure for hard spheres, construed as the infinite-n limit for pair potentials (a/r)n. Methods used are both analytical and simulational, the latter involving molecular dynamics for n=12 and 24. Results show that inherent structures in the hard-sphere limit are randomly packed configurations, where particle radii have been inflated to the point of jamming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449840
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  • 7
    Electronic Resource
    Electronic Resource
    Energy landscape diversity and supercooled liquid properties (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 3353-3361 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Families of model "rugged landscape" potential energy functions have been constructed and examined, in order to clarify the molecular-level basis for the relationship between thermodynamic and kinetic behaviors of glassforming substances. The general approach starts by forming elementary basin units, each of which contains a single local minimum (inherent structure). These units are then spliced together to create a continuous composite potential with the requisite number of basins, upper and lower limits, and boundary conditions. We demonstrate by example that this approach creates wide topographic diversity. Specifically, many pairs of model potential functions exist that share identical thermodynamic properties (depth distribution of minima), but drastically different kinetics (overall topography). Thus, within the confines of this purely mathematical exercise, the "strong" versus "fragile" classifications of thermodynamics and of kinetics are logically disconnected. We conclude that the empirically-observed correlation between thermodynamic and kinetic behaviors embodied, for example, in the Adam–Gibbs equation, must rest upon an additional physical principle involving details of interparticle interactions, transcending the purely mathematical aspects of potential energy landscape topography. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1434997
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  • 8
    Electronic Resource
    Electronic Resource
    Chemical reactions in liquids: Molecular dynamics simulation for sulfur (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6460-6469 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combination of two-atom and three-atom interactions has been selected to represent the structural chemistry of sulfur. This model potential exhibits divalency (bond saturation) and leads to the known preference for Sn molecules to form puckered ring structures. Using this representation of the interactions, molecular dynamics calculations have been performed for 1000 sulfur atoms at the experimental liquid density. Short-range order has been calculated for the low-temperature liquid consisting of S8 cyclic molecules, and agrees qualitatively with the (imprecise) available measurements. At elevated temperatures the cyclic S8 molecules in the simulation begin to break open, and their subsequent chemical reactions yield primarily linear polymeric species. A metastable reaction intermediate in the polymerization process has been identified, a "tadpole'' consisting of a diradical chain attached weakly to an S8 ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451426
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  • 9
    Electronic Resource
    Electronic Resource
    Sensitivity of liquid-state inherent structure to details of intermolecular forces (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6413-6418 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Temperature dependence of short-range order has been systematically studied in two model atomic liquids, using molecular dynamics computer simulation linked to steepest-descent mapping of configurations onto potential minima. Owing primarily to differing attractive forces, the natural crystal structures differ for the two models (face-centered-cubic vs primitive hexagonal). Only one of these crystals is geometrically consistent with the number of particles (256) and boundary conditions (periodic, cubic cell) used for both. Nevertheless, both liquids were found to exhibit temperature dependence of short-range order arising solely from vibrational smearing of underlying temperature-independent inherent structure. The latter differs substantially for the two models, and in each case resembles a highly defective version of the corresponding crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449540
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  • 10
    Electronic Resource
    Electronic Resource
    Consequences of the balance between the repulsive and attractive forces in dense, nonassociated liquids (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 3335-3343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Current theories successfully predict the equilibrium structure of many simple liquids near their triple point from the repulsive molecular forces alone. We present a simple model substance whose liquid structure cannot be predicted adequately with only the repulsions. Furthermore, the model's crystal structure changes drastically upon the removal of the attractions. This failure for our model to conform to the accepted picture of simple liquids gives us the opportunity to sharpen the boundary between substances which, respectively, may and may not be expected to so conform. We conclude that the structure of the corresponding solid deserves more weight than is conventionally given by modern theories of liquids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448954
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