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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 443-451 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A self-consistent hybrid Hartree-Fock/density functional method was validated by computing a number of properties for the whole series of neutral and cationic hydrides of first-row transition metals. The binding energies for the cationic species are significantly improved with respect to those provided by standard density functionals, reaching an accuracy comparable to that of the most sophisticated post-Hartree-Fock approaches. The results are slightly worse for neutral species, although the improvement with respect to conventional density functionals is still significant. At the same time, the computed bond lengths and dipole moments are in remarkable agreement with the available experimental data. © 1997 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 361-367 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A parallel MP2 and DFT study was performed for mercury dihalides and for representative organomercury compounds including a Hg(SINGLE BOND)C bond. From a methodological point of view, medium-size basis sets provide reliable general trends for a number of properties already at the HF level. However, quantitative results can only be obtained including correlation energy by post-Hartree-Fock (even at the MP2 level) or density functional models and adding f-polarization functions on Hg. At this level, geometrical parameters are sufficiently accurate for most purposes and reliable thermodynamic data can be obtained using isodesmic reactions. The advantage of the DF approach resides, besides the shorter computation times, in the lower dependence of the results on the basis set. From a more general point of view, all the computations indicate that Hg(SINGLE BOND)C bond breaking is favored, decreasing the electronegativity of further substituents. We have next investigated the reaction mechanism for cleavage of the Hg(SINGLE BOND)C bond by halogenic acids. Our results show that the reaction occurs through a one-step mechanism in which, however, bond forming and breaking are not completely synchronous. © 1997 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 429-442 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report a critical assessment of the building blocks constituting a general protocol for the study of the structure, strength, and kinetics of hydrogen bridges in large biological systems. The potentialities of self-consistent hybrid approaches for computing reliable potential energy surfaces are described and validated for a number of model systems. Combined discrete-continuum models for studying environmental effects are introduced and applied to some case studies. Finally, some aspects about the role of tunneling are discussed. © 1997 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0192-8651
    Keywords: force field ; open-shell amino acids ; peptides ; glycine ; glycine radical ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Parameters suitable for extending the AMBER force field for nucleic acids and proteins to open-shell derivatives of amino acid residues are proposed and tested. Two new atom types (radical carbon [CE] and hydrogen directly bonded to it [HE]) are introduced, whose parameters have been determined by a best fitting of quantum-mechanical computations of the simplest analogue of glycine radical (GlyR) in a peptide. The new force field is able to fit the reference results concerning both the structural parameters and the relative stabilities of the different conformers. It has been next applied to a conformational study of the distortions induced by extraction of the glycine Hα atom in an initially helical structure of a dodecamer of alanine including a central glycine residue. Our results show that the helical structure corresponds to a local energy minimum, but deeper minima are found which correspond to a fully planar GlyR residue included in a distorted helical sequence.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1720-1728, 1997
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 418-429 
    ISSN: 0192-8651
    Keywords: Lacks-Gordon exchange functional ; Lee-Yang-Parr correlation functional ; conventional density functional ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present an analysis of the numerical performances of the exchange functional proposed by Lacks and Gordon, which we have implemented in the Gaussian series of programs. This functional has been built with the double aim of respecting most of the known scaling and asymptotic properties and of giving good numerical performances, especially as concerns noncovalent interactions. We have found that the coupling of the Lacks-Gordon exchange and Lee-Yang-Parr correlation functionals provides a reliable conventional density functional approach. The corresponding parameter-free adiabatic connection model, in which the ratio between Hartree-Fock and Lacks-Gordon exchange is determined a priori from purely theoretical considerations, allows us to obtain remarkable results for both covalent and noncovalent interactions in a satisfactory theoretical scheme, encompassing the free electron gas limit and most of the known scaling conditions.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 418-429, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 404-417 
    ISSN: 0192-8651
    Keywords: geometry optimization ; polarizable continuum model ; density functionals ; fixed cavity ; mobile cavity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A new implementation of analytical gradients for the polarizable continuum model is presented, which allows Hartree-Fock and density functional calculations taking into account both electrostatic and nonelectrostatic contributions to energies and gradients for closed and open shell systems. Simplified procedures neglecting the derivatives of the cavity surface and/or using single spheres for XHn groups have also been implemented and tested. The solvent-induced geometry relaxation has been studied for a number of representative systems in order to test the efficiency of the procedure and to investigate the role of different contributions.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 404-417, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1993-2000 
    ISSN: 0192-8651
    Keywords: proton transfer ; solvent effects ; formamide ; adiabatic connection methods ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Structural, thermodynamic, and kinetic aspects of the tautomerization of formamide through direct and solvent-assisted proton transfer have been investigated. Both specific and bulk effects of the solvent play a role in determining the overall result so that only a mixed discrete-continuum model is sufficiently reliable. Structural modifications induced by the solvent are significant, but have only a slight effect on thermodynamic and kinetic quantities. The same remarks apply to the vibrational shifts induced by the solvent.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1993-2000, 1997
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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