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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 7070-7084 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A uniform neutralizing background plasma is employed by default in standard Ewald calculations for net-charged systems. We show here that this plasma leads to serious artifacts in both system energy and pressure, which lead to unrealistic behavior. These artifacts are especially critical to simulations where either net charge or volume is allowed to change. To correct these problems we institute a net-charge correction term that consists of subtracting off the Ewald sum for a single particle with charge equal to the net charge of the full system and an optional Born or Poisson–Boltzmann term. This correction decreases pressure artifacts by three orders of magnitude and allows rapid energy convergence as the cell size increases. The correction term is general, in that it applies to systems of any shape or net charge. The net-charge correction was tested for systems in all three phases of matter: gas, solid, and liquid, and found to be markedly superior to standard Ewald in all three cases. In the gas phase, isolated molecular energies are quickly achieved as the cell size increases. In the solid phase the vaporization energy of the NaCl crystal is reproduced using free energy perturbation techniques where a single atom is removed. In the liquid phase, the solvation free energy of Na+ was investigated. It is demonstrated that both the net-charge correction and an energy term twice the size of a Born term is required to obtain optimal free energies of ionic hydration. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10252-10266 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Statistical ensembles for simulating liquid interfaces at constant pressure and/or surface tension are examined, and equations of motion for molecular dynamics are obtained by various extensions of the Andersen extended system approach. Valid ensembles include: constant normal pressure and surface area; constant tangential pressure and length normal to the interface; constant volume and surface tension; and constant normal pressure and surface tension. Simulations at 293 K and 1 atm normal pressure show consistent results with each other and with a simulation carried out at constant volume and energy. Calculated surface tensions for octane/water (61.5 dyn/cm), octane/vacuum (20.4 dyn/cm) and water/vacuum (70.2 dyn/cm) are in very good agreement with experiment (51.6, 21.7, and 72.8 dyn/cm, respectively). The practical consequences of simulating with two other approaches commonly used for isotropic systems are demonstrated on octane/water: applying equal normal and tangential pressures leads to an instability; and applying a constant isotropic pressure of 1 atm leads to a large positive normal pressure. Both results are expected for a system of nonzero surface tension. Mass density and water polarization profiles in the liquid/liquid and liquid/vapor interfaces are also compared.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 5561-5572 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 101 (1979), S. 1638-1639 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4613-4621 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new method for performing molecular dynamics simulations under constant pressure is presented. In the method, which is based on the extended system formalism introduced by Andersen, the deterministic equations of motion for the piston degree of freedom are replaced by a Langevin equation; a suitable choice of collision frequency then eliminates the unphysical "ringing'' of the volume associated with the piston mass. In this way it is similar to the "weak coupling algorithm'' developed by Berendsen and co-workers to perform molecular dynamics simulation without piston mass effects. It is shown, however, that the weak coupling algorithm induces artifacts into the simulation which can be quite severe for inhomogeneous systems such as aqueous biopolymers or liquid/liquid interfaces.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 2198-2202 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 101 (1979), S. 307-311 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 99 (1998), S. 279-288 
    ISSN: 1432-2234
    Schlagwort(e): Key words: Molecular dynamics ; Biomolecular simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract. Coupled advances in empirical force fields and classical molecular dynamics simulation methodologies, combined with the availability of faster computers, has lead to significant progress towards accurately representing the structure and dynamics of biomolecular systems, such as proteins, nucleic acids, and lipids in their native environments. Thanks to these advances, simulation results are moving beyond merely evaluating force fields, displaying expected structural fluctuations, or demonstrating low root-mean-squared deviations from experimental structures and now provide believable structural insight into a variety of processes such as the stabilization of A-DNA in mixed water and ethanol solution or reversible β-peptide folding in methanol. The purpose of this overview is to take stock of these recent advances in biomolecular simulation and point out some common deficiencies exposed in longer simulations. The most significant methodological advances relate to the development of fast methods to properly treat long-range electrostatic interactions, and in this regard the fast Ewald methods are becoming the de facto standard.
    Materialart: Digitale Medien
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  • 9
    ISSN: 0887-3585
    Schlagwort(e): AIDS ; energy minimization ; enzyme inhibition ; molecular modeling ; protein conformation ; crosscorrelation map ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The dynamic behavior of one 99-residue subunit of the dimeric aspartyl protease of HIV-1 was studied in a 160 psec molecular dynamics simulation at 300 K in water. The crystal structure of one of the identical subunits of the dimer was the starting point, with the aqueous phase modeled by 4,331 explicit waters in a restrained spherical droplet Analysis of the simulations showed that the monomer displayed considerable flexibility in the interfacial portions of the flap (the region which folds over the substrate), the N- and C-0termini, and, to a lesser extent, the active site. The flap undergoes significant motion as an independent rigid finger, but without the cantilever previously reported hi a simulation of the dimer. The N-terminus displayed the greatest fluctuational disorder whereas the C-terminus exhibited the greatest root mean square movement from the crystal structure. The central core of the monomer had a heavy-atom root mean square deviation from the initial structure of about 3.0 Å during the latter half of the simulation. Although this is larger than the 1.6 Å found for comparable simulations of typical globular proteins, the general features of the tertiary structure were preserved over the course of the simulation. Overall, these results indicate that the relaxed structure obtained in these simulations may provide a better model for the tertiary structure of the solvated HIV-1 protease monomer than the subunit conformation seen in the X-ray crystallographic structure of the dimer. Except in the flap region, the design of compounds intended to interfere with dimerization should take this relaxation and the flexibility of the solvated monomer, especially at the termini, into account. © 1993 Wiley-Liss, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 6 (1989), S. 32-45 
    ISSN: 0887-3585
    Schlagwort(e): long range truncation ; molecular dynamics ; myoglobin ; truncation effects ; protein electrostatics ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: This paper considers the effects of truncating long-range forces on protein dynamics. Six methods of truncation that we investigate as a function of cutoff criterion of the long-range potentials are (1) a shifted potential; (2) a switching function; (3) simple atom-atom truncation based on distance; (4) simple atom-atom truncation based on a list which is updated periodically (every 25 steps); (5) simple group-group truncation based on distance; and (6) simple group-group truncation based on a list which is updated periodically (every 25 steps). Based on 70 calculations of carboxymyoglobin we show that the method and distance of long range cutoff have a dramatic effect on overall protein behavior. Evaluation of the different methods is based on comparison of a simulation's rms fluctuation about the average coordinates of a no cutoff simulation and from the X-ray structure of the protein. The simulations in which long-range forces are truncated by a shifted potential shows large rms deviations for cutoff criteria less than 14 Å, and reasonable deviations and fluctuations at this cutoff distance or larger. Simulations using a switching function are investigated by varying the range over which electrostatic interactions are switched off. Results using a short switching function that switches off the potential over a short range of distances are poor for all cutoff distances. A switching function over a 5-9 Å range gives reasonable results for a distance-dependent dielectric, but not using a constant dielectric. Both the atom-atom and group-group truncation methods based on distance shows large rms deviations and fluctuation for short cutoff distance, while for cutoff distance of 11 Å or greater, reasonable results are achieved. Although comparison of these to distance-based truncation methods show surprisingly larger rms deviations for the group-group truncation, contrary to simulation studies of aqueous ionic solutions. The results of atom-atom or group-group list-based simulations generally appear to be less stable than the distance-based simulations, and require more frequent velocity scaling or stronger coupling to a heat bath.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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