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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2791-2799 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Both geometrical flexibility and instantaneously responsive electrical polarization are incorporated into a newly developed 5-site water model that includes one oxygen atom, two partially shielded protons, and two negative charges representing lone pairs. The charges are diffusively distributed. Their values are variable in accordance with the local field. The intramolecular potential function used is the one recently developed by Dang and Pettitt [J. Phys. Chem. 91, 3349 (1987)] for a free water molecule. In order to strengthen the angular dependence of the intermolecular dimer potential, a short-range Morse-type interaction is introduced to represent specific hydrogen bonding interactions. With this model we carry out a classical constant volume molecular dynamics simulation of liquid water at mass density 0.997 g/cm3 and room temperature 298 K. Results for the liquid structure, thermodynamic properties, transport dynamics, dielectric features, and spectroscopic characteristics are presented and compared with the experimental data and other relevant computer simulations. These comparisons show a significant improvement over the 3-site flexible/polarizable model developed earlier at Texas Tech. Though about four times computationally more intensive, the new model is still simple enough to be applied to studies of liquid water in the presence of various types of local perturbations, where electrical fields and orientational effects specifically require geometric flexibility and electrical polarization.
    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 100 (1994), S. 6961-6968 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new class of potential suitable for modeling the adsorption of water on different metal sites is described. The new potentials are simple in form and convenient for use in computer simulations. In their real space form they comprise three parts: A pairwise sum of spatially anisotropic 12-6 potentials, a pairwise sum of isotropic short range potentials, and an image potential. Two modifications of the potential are developed. In the first, the anisotropic potential acts only on the oxygen atom and not on the protons. In the second, the potential acts on all the atoms of the water molecule. In practical calculations it is convenient to transform the potential to a reciprocal space form in the manner described by Steele [Surf. Sci. 36, 317 (1973)]. Adsorption of water at top, bridge, and hollow sites on (100), (110), and (111) surfaces of Pt, Ni, Cu, and Al were studied using two fitting parameters and the results compared with previous theoretical calculations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 4695-4701 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    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 98 (1993), S. 8892-8899 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sensitivity analysis in various thermodynamic properties of liquid water is performed based on two flexible three-site models. It is found that the determinative factors for the Helmholtz free energy and the system internal energy are the gas-phase O–H bond length and the Lennard-Jones radius. The Lennard-Jones radius also plays a predominating role in evaluating the thermodynamic pressure. On the other hand, the statistical entropy, the heat capacity at constant volume, and the thermal pressure coefficient are mainly controlled by the parameters relating to the O–H bond stretching. In addition, the Kirkwood Gk factor is quite sensitive to the cutoff radius in the reaction field geometry. This study helps understand the thermodynamics in liquid water and provides useful hints for further improving the current water models.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4336-4348 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A classical molecular-dynamics simulation of a 1.791 molal aqueous NaCl solution is performed using a flexible/polarizable five-site water model. Through an investigation of the ion-water pair-correlation functions and the relative orientation of the waters of hydration, we are able to study the solvation structure in this moderately concentrated salt solution. Under perturbations from the solvated ions, there appears a considerable reorganization of the water molecules. Some of the original intermolecular hydrogen bonding structure is broken down, as bonding with the neighboring cations and anions takes place. Also considered in this paper are the energetics of hydration, and the effect of ionic perturbations on properties such as the water intramolecular structure and vibrations, and the solution phase dielectric constant. An important conclusion from this work is that, in the NaCl solution studied here, perturbations on the water structure by the ions affect mainly intermolecular orientational properties. Although they may be large, these orientational effects are not sensitively detected by many experimental techniques, such as x-ray diffraction or vibrational spectroscopy.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9047-9053 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have carried out sensitivity analysis studies to identify the most important potential parameters of the SPC and the TIP3P flexible water models in determining three distribution functions of liquid water—the site–site radial distribution functions, the distribution function of the interaction energy of a water molecule with its surrounding [Pu(ub)], and the distribution function of the local electric field at the oxygen of a water molecule projected along the permanent dipole moment vector of the water molecule [Pe(E⋅μ0)]. The site–site radial distribution functions of each water model are most sensitive to the equilibrium O–H bond length (rOH) and the Lennard-Jones radius (σ) of the model. In addition to these two parameters, the cut-off radius (Rcut) in the reaction field geometry and the atomic partial charges are also important in affecting Pu(ub) of each model, especially the wings of the distribution. The oxygen charge affects the low energy wing of Pu(ub) more than the high energy wing, whereas the hydrogen charge mainly affects the high energy wing and has little effect on the low energy wing of the distribution. As for Pe(E⋅μ0), which provides an indirect check of the validity of the effective charge approximation in accounting for molecular polarizability, the leading factors are rOH, σ, and Rcut. These parameters affect the distribution wings of Pe(E⋅μ0) the most. The key advantage of the sensitivity analysis technique is that it provides a systematic and economical means for studying the role of each parameter of a water model in affecting the properties of the model.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0649
    Keywords: 34.80G ; 42.55 ; 52.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experiments on homogeneous initiation of pulsed avalanche discharges in typical XeCl laser mixtures show that the x-ray preionization pulse remains effective after a time delay of the order of 20 μs even at very high gas pressures (∼15 atm). Detailed kinetics analyses indicate that dissociative attachment of HCl is relatively slow during and after the preionization period so that the long effective delay time cannot be attributed to the storage effect of Cl− ions. Instead, the observed phenomenon can be attributed to the long survival time of the free electrons due to relatively slow diffusion and electron-ion recombination. Some problems arising from quantitative interpretation of the experimental results are also noted and discussed.
    Type of Medium: Electronic Resource
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