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  • 1
    Electronic Resource
    Electronic Resource
    A molecular Ornstein–Zernike study of popular models for water and methanol (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1138-1147 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Some effective models of water (TIP3P, SPC, SPC/E, TIP4P) and methanol (OPLS, H1) are studied with the help of the molecular Ornstein–Zernike (MOZ) theory using the hypernetted chain (HNC) approximation. The quality of the results obtained within the HNC approximation is discussed by comparison with values from molecular dynamics (MD) simulations. The MOZ-HNC theory yields internal excess energies and dielectric constants which are about 20% smaller than the simulation results found in the literature. The relative trends of the properties observed by simulation for the different interaction models are correctly predicted. In order to calculate the rotational invariant coefficients which define the liquid structure, new MD simulations were carried out. The rotational invariant coefficients derived from the simulation and from the MOZ theory strongly differ. In particular, the center–center distribution functions show that the theory is not able to reproduce the tetrahedral structure of water. In this solvent a comparison of the O–H distribution function indicates that the MOZ theory underestimates the H bonding. The use of a spherically symmetric bridge function in the reference HNC approximation does not lead to an improvement of the MOZ results. The observed defects of the MOZ-HNC approach contrast with the good agreement found for aprotic solvents and are presumably due to the association by H bonds in water and methanol. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478171
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. II. Charge separation processes (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3643-3657 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new approach to carry out molecular dynamics simulations of chemical reactions in solution using combined density functional theory/molecular mechanics potentials is presented. We focus our attention on the analysis of reactive trajectories, dynamic solvent effects and transmission coefficient rather than on the evaluation of free energy which is another important topic that will be examined elsewhere. In a previous paper we have described the generalities of this hybrid molecular dynamics method and it has been employed to investigate low energy barrier proton transfer process in water. The study of processes with activation energies larger than a few kT requires the use of specific techniques adapted to "rare events" simulations. We describe here a method that consists in the simulation of short trajectories starting from an equilibrated transition state in solution, the structure of which has been approximately established. This calculation is particularly efficient when carried out with parallel computers since the study of a reactive process is decomposed in a set of short time trajectories that are completely independent. The procedure is close to that used by other authors in the context of classical molecular dynamics but present the advantage of describing the chemical system with rigorous quantum mechanical calculations. It is illustrated through the study of the first reaction step in electrophilic bromination of ethylene in water. This elementary process is representative of many charge separation reactions for which static and dynamic solvent effects play a fundamental role. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473458
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  • 3
    Electronic Resource
    Electronic Resource
    The direct experimental determination of a dipole–dipole cross-correlation spectral density (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2212-2216 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel method for ascertaining certain dipolar cross-correlation spectral densities is described in detail. This method is based upon the inherent simplicity associated with the perturbation-initial-response characteristics of various multiplet or multispin magnetizations. Furthermore, it is demonstrated that suitable multipulse sampling sequences can be devised which effectively sequester conventional nuclear magnetization and, hence, facilitate the study of multispin magnetization. The outlined methodology is applied to determine a three-spin cross-correlation spectral density for an adamantyl methylene spin grouping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448364
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