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  • Atomic, Molecular and Optical Physics  (16)
  • Valency of first-row atoms  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Valency. II. Applications to molecules with first-row atoms (1983)
    Springer
    Theoretical chemistry accounts 63 (1983), S. 511-527 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Valency of first-row atoms ; Free valence ; Bond indices ; Natural hybrids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A quantum chemical definition of valency proposed in Part I is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method. It is demonstrated that consistency of the basis set is necessary for comparable results. The general features of valency and bonding in these molecules are discussed. The π-electron concept of free valence is generalised to sigma systems and atoms in molecules are classified as subvalent, normal or hypervalent. The relation between valency and natural hybrid occupancy is illustrated. The symmetry properties of natural hybrid orbitals are discussed by means of group theory. A preliminary attempt is made to relate covalency and covalent reactivity. Bond indices and the σ, π character of bonds are obtained by a suitable partitioning and projection of valency into bonding and antibonding contributions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02394810
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  • 2
    Digitale Medien
    Digitale Medien
    Valency. II. Applications to molecules with first-row atoms (1983)
    Springer
    Theoretical chemistry accounts 63 (1983), S. 511-527 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Valency of first-row atoms ; Free valence ; Bond indices ; Natural hybrids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A quantum chemical definition of valency proposed in Part I is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method. It is demonstrated that consistency of the basis set is necessary for comparable results. The general features of valency and bonding in these molecules are discussed. The π-electron concept of free valence is generalised to sigma systems and atoms in molecules are classified as subvalent, normal or hypervalent. The relation between valency and natural hybrid occupancy is illustrated. The symmetry properties of natural hybrid orbitals are discussed by means of group theory. A preliminary attempt is made to relate covalency and covalent reactivity. Bond indices and the σ, π character of bonds are obtained by a suitable partitioning and projection of valency into bonding and antibonding contributions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00552653
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  • 3
    Digitale Medien
    Digitale Medien
    Extension of semiempirical methods to simulation of surfaces (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 283-295 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Various approaches for surface simulation are described. They are based on free, saturated, and embedded clusters, as well as periodic models. The features of semiempirical methods are reviewed and ideas for their improvement are discussed. Special features of the structure and stability of clusters are presented which are suitable for the transition to the solid state. Linear and nonlinear relationships for binding energies and bond lengths in dependence of the average coordination number are discussed. Finally, a systematic way for the simulation of adsorption at ion crystal surfaces by model clusters is suggested. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Multipole moment analysis for hydrides, fluorides, and lithium compounds of first- and second-row elements (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 295-308 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method is presented that conserves all local dipole moments in a partitioning of overlap charge between pairs of atoms. The approximate conservation of quadrupole and higher-moment components can be used as a criterion for the suitability of atomic basis sets. Ab initio calculations are presented for hydrides, fluorides, and lithium compounds of first- and second-row elements in a systematic study of compounds and basis sets. The best suitable basis set for each series is determined by the criterion of best approximate conservation of quadrupole moment components. A linear relation between charge shifts and Mulliken electronegativity differences is established for diatomic molecules. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560480504
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  • 5
    Digitale Medien
    Digitale Medien
    Is there any three-center CBC bond in 1, 5-C2B3H5 and 1,5-C2B3H3? (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 407-412 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Localized molecular orbitals, two- and three-center bond indices of 1,5-dicarba-closo-pentaborane (5) and 1,5-dicarba-closo-pentaborane (3) and their hydrocarbon analogs bicyclo [1,1,1]-pentane and [1,1,1] propellane, respectively, have been calculated using a suitable basis set. No previously reported three-center CBC bond has been found. However, a new three-center BCB bond has been observed in 1,5-dicarba-closo-pentaborane (5). © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560530406
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  • 6
    Digitale Medien
    Digitale Medien
    Modeling of the mutual molecular polarization with an electronegativity equalization approach (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 563-573 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A model for the mutual polarization of two approaching molecules is proposed, exploiting the principle of electronegativity equalization. The deformation of the electronic density of one molecule is the response to the perturbation of its chemical potential due to the electrostatic potential of the other molecule. The electronic densities, the density deformations, and the electrostatic potentials of both molecules are described with a previously developed asymptotic density model (ADM). The ADM model allows a partitioning of all relevant properties in terms of atomic quantities. The perturbation of the chemical potential is given in atomic resolution, and the change of the electronic density is represented in terms of atomic charges. A hardness tensor, which determines the changes of the atomic chemical potentials due to the changes of the atomic charges, is modeled consistently with the ADM and earlier approaches. The results of the model, the changes of atomic charges within the molecules due to their mutual interaction, are compared with the changes of atomic charges obtained from population analysis of ab initio calculations. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560560513
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  • 7
    Digitale Medien
    Digitale Medien
    Consistent parametrization of semiempirical MO methods (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 517-531 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The parametrization of semiempirical molecular orbital methods is reviewed. The parametrization procedures are classified in three categories. The newly proposed category of consistency of parameters in a row of elements is applied in SINDO1 to the Si atom. The calculations on test molecules and silicon clusters demonstrate that significant improvements in accuracy can be obtained in this way. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560440410
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  • 8
    Digitale Medien
    Digitale Medien
    Valence and hypervalence in compounds with second-row elements (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 687-694 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A recently introduced concept of charge and valence for ab initio wave functions is applied to molecules with second-row elements. Mulliken and Löwdin charges and their valence counterparts by Mayer and Gopinathan-Jug are calculated for selected molecules with 4-31G and 6-31G* wave functions and compared with results derived from the new valence concept. It is concluded that the term hypervalence can be reasonalby used in phosphorus compounds PF5 and PCl5 and sulfur compounds SO3 and SF6.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560410505
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  • 9
    Digitale Medien
    Digitale Medien
    Classification of substituents by σ and π electron energy separation (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 197-206 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The previously introduced σ and π energy separation is extended to subsystems. σ and π electron donor and acceptor properties of the substituents are tested with a Löwdin population analysis. The influence of the substituents on the σ and π electron energies is calculated for substituted benzene, cyclobutadiene, butadiene, and borazine. A linear relationship is found which shows that an increase of σ electron energy is accompanied by a decrease in π electron energy and vice versa. This allows a classification of substituent groups in terms of reactivity. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560490311
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  • 10
    Digitale Medien
    Digitale Medien
    SINDO1 calculations of vibrational frequencies of adsorbed molecules (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 411-417 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A scaling procedure is used for the force constants generated by the SINDO1 method in internal coordinates to achieve better agreement with experimental frequencies of molecules. The procedure is subsequently used to calculate frequency shifts for adsorbed molecules. The results for CO2 and CO adsorption at NaCl cluster surfaces are in good agreement with experimental data. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560550505
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