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  • 1
    Electronic Resource
    Electronic Resource
    Calculation of the entropy of binary hard sphere mixtures from pair correlation functions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2153-2155 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We evaluate the entropy of several binary hard sphere fluid mixtures using two approximate expressions that require as input only the pair correlation functions, gαβ(r). An approximation based on the incompressible limit is found to be accurate for medium to high density fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463103
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  • 2
    Electronic Resource
    Electronic Resource
    The crystal–liquid interface of a body-centered-cubic-forming substance: Computer simulations of the r−6 potential (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3638-3646 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interfaces between a bcc crystal and its melt are studied by molecular dynamics simulation. Three distinct crystal/melt interfaces, (100), (111), and (110) are studied. For all interfaces the variation with z, the coordinate perpendicular to the interfacial plane, of the single particle density (averaged over the directions perpendicular to z) and the diffusion constant are measured. Although the 10–90 widths of the density peak-height profiles differ significantly among the three interfaces (6, 9, and 7 molecular diameters, respectively), the corresponding 10–90 widths of the diffusion constant profiles are nearly identical with a common value of about four molecular diameters. This leads to the conclusion that the differences in apparent structural width are due primarily to geometric considerations and not to differences in average local molecular environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456897
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  • 3
    Electronic Resource
    Electronic Resource
    Weighted-density-functional theory calculation of elastic constants for face-centered-cubic and body-centered-cubic hard-sphere crystals (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2699-2704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isothermal elastic constants for the face-centered-cubic (fcc) and body-centered-cubic (bcc) hard-sphere crystal are calculated for a range of densities using the modified weighted-density functional of Denton and Ashcroft [Phys. Rev. A 39, 4701 (1989)]. The fcc elastic constants are shown to be in excellent agreement with the computer simulation data and to represent a significant improvement over the predictions of other density-functional methods. The bcc crystal is predicted correctly to be unstable to shear, in agreement with simulation. This fact supports the conclusion that the bcc hard-sphere solid, even though mechanically unstable, is well described by such methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463059
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum-mechanical derivation of the Bloch equations: Beyond the weak-coupling limit (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4391-4404 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two nondegenerate quantum levels coupled off-diagonally and linearly to a bath of quantum-mechanical harmonic oscillators are considered. In the weak-coupling limit one finds that the equations of motion for the reduced density-matrix elements separate naturally into two uncoupled pairs of linear equations for the diagonal and off-diagonal elements, which are known as the Bloch equations. The equations for the populations form the simplest two-component master equation, and the rate constant for the relaxation of nonequilibrium population distributions is 1/T1, defined as the sum of the "up'' and "down'' rate constants in the master equation. Detailed balance is satisfied for this master equation in that the ratio of these rate constants is equal to the ratio of the equilibrium populations. The relaxation rate constant for the off-diagonal density-matrix elements is known as 1/T2. One finds that this satisfies the well-known relation 1/T2=1/2T1. In this paper the weak-coupling limit is transcended by deriving the Bloch equations to fourth order in the coupling. The equations have the same form as in the weak-coupling limit, but the rate constants are calculated to fourth order. For the population-relaxation rate constants this results in an extension to fourth order of Fermi's golden rule. We find that these higher-order rate constants do indeed satisfy detailed balance. Comparing the dephasing and population-relaxation rate constants, we find that in fourth order 1/T2≠1/2T1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460626
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  • 5
    Electronic Resource
    Electronic Resource
    On the microscopic nature of inhomogeneously broadened spectra of chromophores in glasses and crystals (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3880-3881 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455796
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  • 6
    Electronic Resource
    Electronic Resource
    Microscopic theory of reversible pressure broadening in hole-burning spectra of impurities in glasses (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3274-3281 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, Sesselmann et al. [Phys. Rev. B 36, 7601 (1987)] have examined the effect of pressure changes on hole-burning spectra of dye molecules in polymer glasses, finding that the hole shift and broadening are linear in the pressure change and its magnitude, respectively. We develop a statistical, microscopic theory of this effect, and of the inhomogeneous line shape itself. In the limit that the density of solvent perturbers becomes large, the general theory predicts that both the inhomogeneous line shape and the hole shape after a pressure change will be Gaussian, in qualitative agreement with experiment. By considering a specific model for the solute–solvent interaction, we then provide a quantitative analysis of the experiments that shows that the pressure broadening is due to changes in the local environment of each chromophore. As a further test of the theory, we make a prediction as to the frequency dependence of the pressure-dependent hole shift, which can be easily tested by experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455881
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  • 7
    Electronic Resource
    Electronic Resource
    T2 can be greater than 2T1 even at finite temperature (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4405-4410 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relaxation of a nondegenerate two-level quantum system linearly and off-diagonally coupled to a thermal bath of quantum-mechanical harmonic oscillators is studied. The population and phase relaxation times, T1 and T2, are calculated to fourth order in the system/bath interaction. Focus is on a specific model of the bath spectral density that is both Ohmic (proportional to frequency at low frequency) and Lorentzian, and which has the property that, in the semiclassical or high-temperature limit, it reproduces the stochastic model studied previously by Budimir and Skinner [J. Stat. Phys. 49, 1029 (1987)]. For this fully quantum-mechanical model, it is found that under certain conditions the standard inequality, T2≤2T1, is violated, demonstrating that this unusual result, which was originally derived from the (infinite-temperature) stochastic model, is valid at finite temperature as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460627
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  • 8
    Electronic Resource
    Electronic Resource
    Entropy of electrolytes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3775-3779 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The entropy of 1–1 and 2–2 model electrolytes is calculated from an expansion in terms of the multiparticle correlation functions. For electrolytes, a simple truncation of this expansion is never sufficient for the accurate calculation of the entropy, even in the limit of low concentration, in marked contrast to the behavior for short-ranged potentials. However, a partial, but infinite-order, summation of the expansion is shown to yield both the correct low-concentration limit and excellent results over a wide range of concentrations for both 1–1 and 2–2 electrolytes. The consequences of this result for some earlier applications of the entropy expansion to electrolytes are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466365
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  • 9
    Electronic Resource
    Electronic Resource
    On the ratio T2/T1 for non-Ohmic spectral densities (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 852-852 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Defining T1 and T2 to be the population and phase relaxation times, respectively, for a two-level system coupled to a bath, previous work for Ohmic spectral densities has shown, surprisingly, that in some instances T2(approximately-greater-than)2T1. This note shows that this inequality can also be realized for non-Ohmic spectral densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468089
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  • 10
    Electronic Resource
    Electronic Resource
    The role of localization in glasses and supercooled liquids (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5199-5208 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Localized excitations (tunneling modes, soft harmonic vibrations) are believed to play a dominant role in the thermodynamics and transport properties of glasses at low temperature. Using instantaneous normal-mode (INM) analysis, we explore the role that such localization plays in determining the behavior of such systems in the vicinity of the glass transition. Building on our previous study [Phys. Rev. Lett. 74, 936 (1995)] we present evidence that the glass transition in two simple model systems is associated with a transition temperature below which all un- stable INM's become localized. This localization transition is a possible mechanism for the change in diffusion mechanism from continuous flow to localized hopping that is believed to occur in fragile glass formers at a temperature just above Tg. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471147
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