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  • American Institute of Physics (AIP)  (54)
  • American Society of Hematology  (38)
  • American Chemical Society (ACS)  (31)
  • 1
    Publication Date: 2024-05-03
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2553-2560 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometries, energetics, and some first and second order molecular properties (dipole moments, force constants, polarizabilities) of small stoichiometric (NaCl)n and nonstoichiometric (NanCln−1), n≤4 clusters were studied at the SCF and various correlated levels.
    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 91 (1989), S. 2818-2833 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three-dimensional potential energy and electric dipole moment functions for the electronic ground state of H2O+ have been calculated from highly correlated multiconfiguration reference configuration interaction (MRCI) electronic wave functions. The analytic representations of these functions have been used in vibrational and perturbational calculations of the rovibrational absorption spectrum of H2O+. The quartic force fields in normal coordinates have been employed in the evaluation of the equilibrium spectroscopic constants in H2O+, D2O+, and HDO+ by perturbation theory. The equilibrium structure, vibrational band origins, centrifugal distortion constants and rotational energy levels agree very well with the available experimental data. Absolute vibrational band intensities have been calculated from the dipole moment functions and are compared with theoretical integrated band intensities. The radiative lifetimes of excited vibrational states exhibit mode specific variations. The rotationally resolved room temperature absorption spectra have been evaluated ab initio for the pure rotational and the ν2, 2ν2, ν1, ν3, and 3ν2 transitions. The rovibrational electric dipole transition matrix elements and absolute line intensities are given for the most intense transitions. These data take full account of anharmonicity effects and vibration–rotation coupling.
    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 96 (1992), S. 4551-4558 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations of a system of 2500 parallel cut spheres of thickness L/D=0.1 give evidence for a phase transition, at packing fraction η∼0.40, from the low density nematic phase to a smectic phase. No tendency to formation of columnar ordering is observed up to densities as high as η=0.60. This behavior contrasts with that of freely rotating cut spheres for which the sequence of stable phases has been identified as isotropic–nematic–columnar–solid [D. Frenkel, Liquid Cryst. 5, 929 (1989)]. For the present system of highly anisotropic molecules the slow convergence of the expansion of correlation functions on rotational invariants precludes quantitative comparison between integral equation theory and simulation results.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6818-6832 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Extensive Monte Carlo simulation results for the pair and triplet direct correlation functions of the one-component, hard-sphere system near freezing are presented. These results are in good agreement with the analytic predictions of a recently derived free energy density functional for the inhomogeneous hard-sphere fluid. This free energy model is based on the fundamental geometric measures of the particles. It provides the first unified derivation of the analytic description of the hard-sphere thermodynamics and pair structure as given by the scaled-particle and Percus–Yevick theories, and yields simple explicit expressions for the high order direct correlation functions of the uniform fluid.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3197-3205 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamic, dielectric, and structural properties of systems of dipolar hard spherocylinders and ellipsoids with perfect nematic order are investigated by means of the hypernetted chain (HNC) equation. The density, temperature domain for which the HNC equation admits a stable solution is determined. For spherocylinders a large increase of the main peak of the total structure factor in the vicinity of the stability limit of the HNC equation is, tentatively, associated with the onset of a nematic–smectic-A transition. The situation seems less clear for dipolar ellipsoids, though the results are in many aspects qualitatively similar to the spherocylinder case. The pair structure near the transition is analyzed. It is not characteristic of any of the smectic-A phase structures typical of strongly polar liquid crystals. This is probably a consequence of the highly symmetric nature of the model.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6635-6644 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Highly correlated CEPA electronic wave functions have been used to calculate the three-dimensional potential energy and electric dipole moment functions of the X 1A' and a 3A‘ states of HCF. The analytic expansions of these functions have been employed in variational and perturbational calculations of the vibrational band origins and spectroscopic constants. For the singlet ground state the vibrational band origins agree with available experiments to within 2 to 20 cm−1, the rotational constants to within 0.04 cm−1. Theoretical spectroscopic constants of similar accuracy are presented also for the triplet state. The singlet–triplet separation is calculated to be 13.9 kcal/mol, in agreement with the experimental upper bound of 14.7±0.2 kcal/mol. The dipole moments (μ0) have been calculated to be 1.394±0.05 D (X 1A') or 1.049±0.05 D (a 3A‘), respectively, and vibrational radiative transition probabilities are also given. Anomalous variations of radiative lifetimes in some low-lying vibrational levels have been found in the singlet state of HCF which are due to anharmonic coupling effects.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7403-7411 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hypernetted chain (HNC) and Percus–Yevick (PY) integral equations are solved numerically for parallel hard spherocylinders of length-to-width ratios L/σ ranging from 0.5 to 5.0. The PY virial pressure is in excellent agreement with Monte Carlo data. The HNC equation gives evidence for the existence of a nematic to smectic-A phase transition at densities which compare reasonably well with the Monte Carlo (MC) estimates, whereas the PY equation gives stable nematic solutions for densities beyond the MC transition densities. For a given packing fraction η, pressure and pair correlation functions (properly scaled) depend very little on the elongation L/σ in the range 3–5.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6941-6946 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isotropic–nematic phase transition is investigated for several model liquid crystals using the density functional method. The models considered are hard ellipsoids of revolution (both prolate and oblate cases), hard spherocylinders, and two additional fluids characterized by pair potentials of a generalized Maier–Saupe type. The direct pair correlation functions for the isotropic phase are obtained by numerical solution of the hypernetted-chain (HNC) and Percus–Yevick (PY) integral equation theories. It is shown that second order density functional theory is strongly dependent upon the approximation used for the isotropic direct pair correlation function. In all cases the density functional results are qualitatively consistent with conclusions based upon orientational stability criteria.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3096-3100 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply integral equation theory to the calculation of the thermodynamics and the distribution functions of a mixture of hydrogen atoms and molecules at high densities and temperatures. The integral equations are found to tackle very efficiently the problem of the softness and the nonadditivity of the potentials, as encountered under these conditions, and give better results than hard sphere perturbation theory. Comparison with Monte Carlo calculations show that the so-called HMSA and modified hypernetted chain (MHNC) equations, give almost perfect results. This extends the range of validity of these schemes to domains of high pressures and temperatures.
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