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  • Engineering  (3,321)
  • Computational Chemistry and Molecular Modeling  (2,365)
  • 1990-1994  (5,686)
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Year
  • 11
    Electronic Resource
    Electronic Resource
    The PPP-CI scheme as a fundamental physical model (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 497-508 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Parametrized computational procedures and simplified physical models of molecular reality are often related to one another but are by no means the same thing. With special reference to work by Koutecky and by Cizek, Paldus et al., it is shown here that the PPP model rests on a simple but physically sound electrostatic picture of a molecular π system, and its intrinsic difference from an independent particle model is emphasized. As an illustration of the heuristic power which makes physical models powerful tools of theoretical research, ground state charge transfer GSCT, in situ molecular electronegativity, and the principle of electronegativity equalization are derived within the PPP-CI scheme, no use being made of molecular orbitals, and the assumptions on which the CT theory rests are made explicit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370418
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  • 12
    Electronic Resource
    Electronic Resource
    Quantum-chemical investigation of Buckminsterfullerene and related carbon clusters (I): The electronic structure and UV spectra of Buckminsterfullerene, and other C60 cagesWith great admiration and respect for the contributions that Drs. Pariser, Parr, and Pople have made throughout their careers and in particular for helping to organize our thoughts on molecular electronic spectra and for supplying quantum chemistry with its most beloved model Hamiltonian. (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 599-607 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of C60 cages are examined by use of the INDO and INDO/CI methods. The calculated spectrum of Buckminsterfullerene has one allowed low-lying band at 27,300 cm-1, to be compared with an experimental value of 25,900 cm-1. These calculations suggest that other cage structures are not stable, or they are not ground state singlets.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370426
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  • 13
    Electronic Resource
    Electronic Resource
    The use of localized molecular orbitals and the polarization propagator to identify transmission mechanisms in nuclear spin-spin couplings (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 663-677 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extension of the IPPP (inner projections of the polarization propagator) method to theoretically analyze transmission mechanisms of indirect nuclear spin-spin couplings is presented. The localization technique used is modified so that all the canonical molecular orbitals of a compound may be localized to represent chemical bonds, lone pairs, and the corresponding antibonding molecular orbitals. These localized molecular orbitals, together with the polarization propagator, are used to obtain an intuitive picture of how a coupling is generated as a sum of terms, each one consisting of two particle-hole single excitations. This picture can be used to identify underlying transmission mechanisms and quantitatively evaluate their importance toward the total coupling. The paramagnetic spin-orbit and the spin-dipole interactions are studied in detail.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370505
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  • 14
    Electronic Resource
    Electronic Resource
    Computational models for proton transfer in biological systems (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 701-711 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A computational scheme based on a “mixed basis set” approach is applied to the study of the structure and the energetics in proton transfer systems. Five hydrogen-bonded systems of the type (CH3HnA ‥ H ‥ BHmCH3)+, where A and B can be N, O, or S, have been investigated with various minimal and extended basis sets. Calculations with the extended basis set yield double-well potential energy curves, which the minimal basis set is unable to reproduce. Calculations with the mixed basis set, constructed from an extended basis set on the atoms engaged in the hydrogen transfer part and a minimal basis set on the rest of the molecule, give predictions of geometries, potential energy curves, and relative energies similar to the results from the extended basis set. Inclusion of polarization functions in the mixed basis set becomes essential in systems that contain third row atoms. This scheme should become useful in studies of large molecules in which different parts can be represented at different levels of computational complexity.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370508
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  • 15
    Electronic Resource
    Electronic Resource
    How to find a saddle point (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 773-783 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper explains a method for finding saddle points on a multidimensional surface and shows how it may be used to define saddle-point seeking curves that have properties similar to well-known orthogonal trajectories. It is shown that a gradient extremal is a special case of one of these curves, and its chemical significance as the path, defined by local criteria, which starts from a stable structure and leads to a transition state, is discussed briefly in relation to the intrinsic reaction coordinate. It is emphasized that this theory gives a natural method for locating points that have Hessians of similar structure to those of transition states.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370606
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  • 16
    Electronic Resource
    Electronic Resource
    Roothaan's open shell theory from the viewpoint of an orthogonal group (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 753-771 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Explicit equations for the constants a and b of the energy as the average expectation value for the minimal domain of states giving the Roothaan energy functional are derived in terms of the total spin value and the “seniority” quantum number. The state with off-diagonal long-range order can appear in the framework of the Roothaan scheme for the quasidegenerate system as an alternative to the Hund rule. Admissible many-electron states are established for all configurations of the icosahedral symmetry group systems, and corresponding a and b coefficients are calculated.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370605
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  • 17
    Electronic Resource
    Electronic Resource
    The correlation potential for two-electron atomic ions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 811-819 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The correlation potential is computed for two electron atomic ions with atomic numbers from 1 to 10 using the charge density reconstructed from a natural orbital expansion of a Kinoshita-like atomic wave function. Over the wide range of densities involved, the correlation potentials are not even approximately a local function of the density.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370609
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  • 18
    Electronic Resource
    Electronic Resource
    The symmetrized basis function method for SU(2) and its application to the total spin states of many-electron systems (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 41-53 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, the symmetrized basis function method is extended and used for the classification of the total spin states of many-electron systems. The reduction matrix, which is expressed as a series of products and direct products of matrices is derived. It is very advantageous that the method can be completed by computer. As an example, the reduction matrix for a 5-electron system calculated by IBM PC computer and the classification of the total spin states is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380105
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  • 19
    Electronic Resource
    Electronic Resource
    The TST-CEQ calculations on the heavy-light-heavy Cl + HCl reaction (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 75-83 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, the TST-CEQ calculated results including the reactive cross sections and rate constants for the Cl + HCl reaction at the specified vibrational state of the HCl are presented. It is shown that the oscillatory behavior of the system in the three-dimensional world does not appear, and the larger the vibrational quantum number of HCl, the smaller the cross sections ¯QTST-CEQ (E, ν) are at a given total energy used in the calculations, but the larger the reactive rate, constants KTST-CEQ (T, ν) are at a given temperature. The KTST-CEQ (T, v) is the same as when first published, and the average reactive rate constants KTST-CEQ (T) are close to the ones by Garrett and Schatz et al.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380107
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  • 20
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380301
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