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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , 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 105 (1996), S. 4197-4210 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In order to avoid the computational expense required to obtain precise numerical solutions of the Poisson–Boltzmann equation, different hypotheses have been introduced which led to less rigorous, but fast and simple solvation models. However, few systematic studies of the predictive features of such models have been reported. Comparisons between different continuum models are made difficult by the large variety of simplifying hypotheses or thermodynamic reference states used by their authors, so that the relationships between the proposed solvation terms is not straightforward. In the present work we consider various continuum models whose common feature is the description of the solvation process in terms of displacement of the high dielectric solvent by the low dielectric molecular bulk. We adapt these different models to work within the frame of the nonlinear fit algorithm developed in our previous study. This leads to a benchmark allowing to run rigorous comparative tests between all the different schemes. The unification of these allows us to derive new solvent models that combine the advantages of the original ones. We address also the problem of the optimal parametrization of the solvation terms and propose a new strategy of assignment of the atomic radii. It is shown that the exact solvation energies, which are in theory linearly related to the solvent displacement terms, cannot be expressed as a linear combination of the displacement effects evaluated with the usual simplifications. Nevertheless, nonlinear empirical models based on these simplified displacement terms are found to yield high quality predictions of vacuum-to-water transfer energies. © 1996 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 104 (1996), S. 6679-6695 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A series of different simplifications of the boundary element method (BEM) for solving the Poisson–Boltzmann equation is investigated in an effort to obtain an accurate and fast enough treatment of electrostatic effects to be incorporated in Monte-Carlo and molecular dynamics simulation methods. The tested simplifications include increasing the size of Boundary Elements, decreasing the surface dot density, and ignoring the interactions between the polarization charges. Combined with terms describing the nonelectrostatic solvation effects, the simplified BEM polarization terms were built into expressions for the solvation potential. The solvation potential is treated as empirical consistent force field equations. The intervening parameters, including atomic and probe radii, are derived by different fitting strategies of calculated vs experimental vacuum to water transfer energies of 173 charged, polar, and nonpolar small molecules. These fits are shown to yield very good correlations (rms ∼1.4 kcal/mol), even when the interactions between the polarization charges are neglected, proving that the most time-consuming step in BEM, which involves solving the linear system, can be successfully avoided. Finally, the computing efficiency of the method is tested on macromolecules and is found to be convenient for implementation in molecular dynamics or Monte Carlo simulations. © 1996 American Institute of 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. 1566-1578 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics and Monte Carlo simulations were carried out for xenon atoms dissolved in liquid benzene in order to study the quadrupolar relaxation mechanism of the xenon-131 nucleus. We confirm that a proper description of the relaxation is obtained by taking into account the quadrupole moment of benzene molecules. In contrast to the Xe–water system, the cross-correlation contribution to the electric field gradient (experienced by the Xe nucleus) is negligible in benzene, and the time correlation function of the total electric field gradient shows a relatively smooth decay. Several molecular motions take part in this decay, but not with the same efficiency. The major contribution can be attributed to the rotation of the benzene molecules around their C2 axes. The adequacy of the Sternheimer model for quadrupolar interactions is confirmed with ab initio calculations. Some methodological aspects of simulations are also discussed, such as the use of a termination function to treat the electrostatic interactions and the effect of the xenon interaction parameters on the simulated relaxation rate.
    Type of Medium: Electronic Resource
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