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  • 1
    Digitale Medien
    Digitale Medien
    Lattice-sum methods for calculating electrostatic interactions in molecular simulations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3014-3021 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: When simulating a periodic molecular system, lattice sum methods may be used to evaluate the electrostatic interactions without resorting to an unphysical truncation of the potential. In a previous publication, we compared the computational efficiency of the Ewald and Particle-Particle Particle-Mesh (PPPM) lattice-sum methods. Because the PPPM method discretizes the field equations and utilizes the highly efficient fast Fourier transform algorithm, it requires significantly less computational effort than the Ewald method and scales almost linearly with system size. In this paper, we take a more detailed look into the theory behind the lattice-sum methods to clarify the underlying similarities between the Ewald method and the PPPM method. We also investigate the errors introduced by different approximation used in the discretization of the field equations in the PPPM method. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470490
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  • 2
    Digitale Medien
    Digitale Medien
    A generalized reaction field method for molecular dynamics simulations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5451-5459 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Molecular dynamics simulations of ionic systems require the inclusion of long-range electrostatic forces. We propose an expression for the long-range electrostatic forces based on an analytical solution of the Poisson–Boltzmann equation outside a spherical cutoff, which can easily be implemented in molecular simulation programs. An analytical solution of the linearized Poisson–Boltzmann (PB) equation valid in a spherical region is obtained. From this general solution special expressions are derived for evaluating the electrostatic potential and its derivative at the origin of the sphere. These expressions have been implemented for molecular dynamics (MD) simulations, such that the surface of the cutoff sphere around a charged particle is identified with the spherical boundary of the Poisson–Boltzmann problem. The analytical solution of the Poisson–Boltzmann equation is valid for the cutoff sphere and can be used for calculating the reaction field forces on the central charge, assuming a uniform continuum of given ionic strength beyond the cutoff. MD simulations are performed for a periodic system consisting of 2127 SPC water molecules with 40 NaCl ions (1 molar). We compare the structural and dynamical results obtained from MD simulations in which the long range electrostatic interactions are treated differently; using a cutoff radius, using a cutoff radius and a Poisson–Boltzmann generalized reaction field force, and using the Ewald summation. Application of the Poisson–Boltzmann generalized reaction field gives a dramatic improvement of the structure of the solution compared to a simple cutoff treatment, at no extra computational cost. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.469273
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  • 3
    Digitale Medien
    Digitale Medien
    Space-time correlated reaction field: A stochastic dynamical approach to the dielectric continuum (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6068-6075 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: In molecular dynamics (MD) simulations, the continuum description of electrostatic interactions has been based in most cases on the static response of the dielectric continuum. In this work, a time-dependent reaction field expression including stochastic and friction terms is derived in analogy to the generalized Langevin equation involving hydrodynamic interactions. Simulations of water using the extended simple-point charge model have been performed under different boundary conditions. The effects of a time-dependent treatment of the reaction field are demonstrated by comparing the results to those of MD simulations using a static, instantaneous reaction field and of MD simulations employing the Ewald sum. It is shown for the first time that the straight cutoff approach not only leads to a disruption of the time, but also of the spatial correlation of the dipole moment. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473269
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  • 4
    Digitale Medien
    Digitale Medien
    Diastereoselective Michael Additions of Chiral Imidazolidines to Trityl Enones (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1145-1151 
    Details
    ISSN: 0170-2041
    Schlagwort(e): Enones ; Trityl enones ; Michael additions ; EPC synthesis ; Pentanols, 4,5-diamino- ; Ethylenediamine, enantiomerically pure N,N-acetals of ; Propionic acids, 2,3-diamino- ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The enolates A and C of t-butyl (R)-2-t-butyl-3-methyl-4-oxo-1-imidazolidinecarboxylate (1, Boc-BMI) and of 1-t-butyl 5-methyl (2R,5S)-2-t-butyl-3-methyl-1,5-imidazolidinedicarboxylate (3) and t-butyl (R)-2-t-butyl-5-lithio-3-methyl-1-imidazolidinecarboxylate (B, from 2) add in a Michael-type reaction to trityl enones (E, 4, 5). With one exception (product 8) a single diastereoisomer is formed (≫98% ds).  -  In two cases (6, 10), the crystal structures of the products are determined by X-ray diffraction. The steric course of the reactions (the relative topicity is unlike with the enolates) is discussed and compared with that of other conversions of the same reagents.  -  The trityl groups of two adducts (8 and 9) are cleaved off by treatment with LiBH4/cat. LiBHEt3 to give diaminopentanol derivatives (12 and 13).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.1992199201188
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