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  • 1
    Electronic Resource
    Electronic Resource
    Mixed lead-alkali clusters in the gas phase and in liquid alloys (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 341-348 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio density functional calculations for NanPb, LinPb, NanPb4, and LinPb4 are reported. The abundance of Na6Pb observed in gas-phase experiments is explained as a consequence of evaporative cooling, which stops at Na6Pb because of the high evaporation energy of this cluster. Insight is also provided into the clustering in the liquid Li-Pb and Na-Pb alloys. Anomalies in several electronic, structural, and thermodynamic properties were detected at certain compositions (20% Pb in Li-Pb; 20% Pb and 50% Pb in Na-Pb) and our calculations support the interpretation of those anomalies in terms of the formation of octet and Zintl clusters.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 341-348, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Ionic vibrational breathing mode of metallic clusters (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 613-626 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The energy of the vibrational mode with spherical symmetry, in which the ionic cores oscillate in the radial direction around the equilibrium geometry (ionic breathing mode) is calculated for trivalent (AlN, 2≤N≤50) and monovalent (NaN, 2≤N≤73; CsN, 2≤N≤74) metallic clusters. The ground-state total energy is calculated using density functional theory, with a spherically averaged pseudopotential to describe the ion-electron interaction and optimizing the geometry by the simulated annealing technique. The energy of the ionic mode is calculated by diagonalization of the dynamical matrix including the electronic relaxation in the linear response approximation. The compressibility and bulk modulus of the metallic cluster are obtained from the energies of the monopole oscillations. These energies present a linear behavior on the inverse of the cluster radius, which is analyzed using a semiclassical liquid drop mass formula for the total energy of the clusters and a scaling model. The values of the vibrational frequencies present electronic shell closing effects for the three metals.©1997 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of environment on proton-transfer mechanisms in model triads from theoretical calculations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1675-1688 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have carried out theoretical calculations to analyze molecular interactions and proton transfer mechanisms in the formate-imidazole-water system, which may be considered the simplest model of catalytic triads in serine proteases. Computations were carried out at the density functional theory level. The effect of a dielectric environment on energy surfaces is considered using a polarizable continuum model and the self-consistent reaction field approach. The role played by inertial and noninertial polarization of this environment is emphasized. Nonequilibrium solvation effects have been estimated. The results show that there are different reaction mechanisms, concerted or stepwise, that may be competitive, depending on the nature of the molecular environment.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1675-1688, 1998
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Theoretical study of ester enolate-imine condensation route to β-lactams (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1826-1833 
    Details
    ISSN: 0192-8651
    Keywords: quantum-chemical computations ; β-lactams ; ester enolate-imine condensation ; solvent effect ; stepwise process ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The condensation reaction of the enolate of methyl acetate with formaldimine to afford a β-lactam was studied using the MP2-FC/6-31+G* level of theory taking into account the electrostatic effect of the solvent by means of a self-consistent reaction field continuum model. The reaction is a stepwise process with three main steps: the formation of the C3(SINGLE BOND)C4 bond, the closure of the β-lactam ring, and the elimination of the methoxide ion. The formation of the C3(SINGLE BOND)C4 bond is rate determining and according to our calculations is not a reversible step.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1826-1833, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    A coupled density functional-molecular mechanics Monte Carlo simulation method: The water molecule in liquid water (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 19-29 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A theoretical model to investigate chemical processes in solution is described. It is based on the use of a coupled density functional/molecular mechanics Hamiltonian. The most interesting feature of the method is that it allows a detailed study of the solute's electronic distribution and of its fluctuations. We present the results for isothermal-isobaric constant-NPT Monte Carlo simulation of a water molecule in liquid water. The quantum subsystem is described using a double-zeta quality basis set with polarization orbitals and nonlocal exchange-correlation corrections. The classical system is constituted by 128 classical TIP3P or Simple Point Charge (SPC) water molecules. The atom-atom radial distribution functions present a good agreement with the experimental curves. Differences with respect to the classical simulation are discussed. The instantaneous and the averaged polarization of the quantum molecule are also analyzed. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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