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  • Computational Chemistry and Molecular Modeling  (14)
  • Point charge models  (5)
  • 1
    Electronic Resource
    Electronic Resource
    The approximation of electron densities (1986)
    Springer
    Theoretical chemistry accounts 69 (1986), S. 63-69 
    Details
    ISSN: 1432-2234
    Keywords: Electron density ; Gaussian 80 ; Point charge models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper discusses the approximate representation of the electron density produced by an ab initio calculation. A linear combination of Gaussians is fitted to the density by minimizing a functional which is the consequent error in field-energy. The practical implementation of the procedure, following a Gaussian 80 calculation, is described and some of the complications are analysed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526293
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  • 2
    Electronic Resource
    Electronic Resource
    Point charge models for LiH, CH4, and H2O (1973)
    Springer
    Theoretical chemistry accounts 31 (1973), S. 311-324 
    Details
    ISSN: 1432-2234
    Keywords: Point charge models ; One-electron properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Point charge models for LiH. CH4, and H2O are presented. The models preserve the correct total charge and dipole moment of the molecules. Relations between spherical Gaussian wave function values and point charge model values of a variety of one-electron molecular properties are derived. The errors inherent in some of the point charge model values are of two types: those which may be large but are easily evaluated and those which are small and diminish rapidly as the distance from the molecule increases. The models are shown to be a reliable means of calculating one-electron properties and possible uses of the models are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527558
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  • 3
    Electronic Resource
    Electronic Resource
    The electron density of the water molecule (1986)
    Springer
    Theoretical chemistry accounts 69 (1986), S. 71-81 
    Details
    ISSN: 1432-2234
    Keywords: Electron density ; Gaussian models ; Point charge models ; Water molecule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electron density of the water molecule, as calculated by a standard program, is approximated by linear combinations of spherical Gaussians. The accuracy of the result is studied as a function of the numbers and positions of the Gaussians. Since this shows where the charge is located in the molecule it has immediate physical significance. The building-up of the density can be followed in more and more detail. From these expansions, point charge models of water are readily deduced. These are compared with models of similar kinds used by other authors. Some of the calculations have been repeated with a wavefunction of higher accuracy to investigate the stability of the results. Results show that the more accurate density requires more Gaussians to represent its greater complexity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526294
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The molecular electrostatic potential of some simple molecules (1986)
    Springer
    Theoretical chemistry accounts 69 (1986), S. 425-436 
    Details
    ISSN: 1432-2234
    Keywords: Molecular electrostatic potential ; Gaussian models ; Point charge models ; Water molecule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The calculation of the molecular electrostatic potential from simplified models of the electron density is considered. Results are shown for water, hydrogen fluoride and ammonia. Little loss of accuracy is evident when the density is represented by a linear sum of well-chosen Gaussians. When these are further simplified into sets of point charges the inner parts of the molecule are poorly represented. More elaborate point moments make the representation worse. On the other hand a mixed representation with point charges and one diffuse Gaussian gives all the essential features of the potential of these molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526701
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  • 5
    Electronic Resource
    Electronic Resource
    The currant bun model of simple molecules (1986)
    Springer
    Theoretical chemistry accounts 70 (1986), S. 257-264 
    Details
    ISSN: 1432-2234
    Keywords: Point charge models ; Polarizability ; Dispersion forces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The model of a molecule previously introduced by the authors, in which most of the electronic charge is represented by point charges on the nuclei, in the lone pairs and bonds, and the remainder is in a diffuse function which represents the outer electrons, is here extended. Molecules with several heavy atoms require several diffuse functions, one for each heavy atom, in addition to one at the centre of nuclear charge. In an electric field the centre of each diffuse function moves against a harmonic restoring force and this gives rise to the polarizability of the molecule. When two molecules interact the movement of this function produces the dispersion force. The model thus embodies all the long range forces between molecules in a more accurate and simpler way than was possible earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00534234
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular modelling with spherical Gaussians (1970)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 533-539 
    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 mathematical model of a molecule is proposed. The electronic structure is described using a molecular orbital wave function constructed from a small number of spherical Gaussians with optimized parameters. The models exhibit the desirable properties of numerical stability, objectivity and transferability. Results are given for CH4, C2H6, cyclo-propane, H2O, CH2O and C2H4. They can be given a chemical interpretation in terms of chemical bonds, lone pairs and atomic cusps.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560040508
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Gauge invariant gaussian orbitals and the ab initio calculation of diamagnetic susceptibility for molecules (1973)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 15-25 
    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: It is shown that gauge terms can be introduced into the Gaussian functions used as the basis functions for an ab initio calculation of the energy of a molecule in the presence of a uniform magnetic field so that all the integrals become independent of the origin of the vector potential. The perturbation treatment of the diamagnetic susceptibility is considered in the molecular orbital approximation. The results show that the susceptibility can be calculated using only the unperturbed orbitals and their first-order corrections. All the integrals that arise can be expressed in terms of known functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560070104
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Symmetry properties of one- and two-electron molecular integrals (1971)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 5 (1971), S. 657-668 
    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 maximum numbers of distinct one- and two-electron integrals that arise in calculating the electronic energy of a molecule are discussed. It is shown that these may be calculated easily using the character table of the symmetry group of the set of basis functions used to express the wave function. Complications arising from complex group representations and from a conflict of symmetry between the basis set and the nuclear configuration are considered and illustrated by examples.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560050606
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  • 9
    Electronic Resource
    Electronic Resource
    Fitting electron densities of molecules (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 881-890 
    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: Compact, convenient expressions for the electron density are derived using a fitting functional. Results are given for H2O, CH4, HF, NH3, and PH3, and show the accuracy obtainable using differing numbers of functions on each center. The definition of an atomic charge using these expressions is discussed and it is shown that the Bader virial-partitioning definition, in which the density is integrated over a volume around each nucleus, leads to convergent results.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250510
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  • 10
    Electronic Resource
    Electronic Resource
    A minimum principle for molecular systems allowing the use of discontinuous wave functions (1970)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 5-20 
    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 minimum principle proposed for atomic systems by Hall, Hyslop and Rees [1] is generalized to molecules. It is shown that this generalization retains the advantage of admitting the use of a larger class of trial wave functions, for example those with discontinuities, than is possible in the usual minimum energy principle. The further advantage that the upper bounds obtained by this treatment are always at least as good as those of the Rayleigh-Ritz method is also preserved.The theory is applied to the H2+ ion, potential energy curves are obtained for various “cut-off” wave functions, and the equilibrium internuclear distance is calculated. The optimization of the “cut-off” region so that the upper bound is minimized is also discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560040103
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