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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 86 (1993), S. 167-179 
    ISSN: 1432-2234
    Keywords: Correlation ; Properties ; Polarization propagator ; Coupled Hartree-Fock ; Random phase approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We consider various possibilities for the uncorrelated reference for the calculation of properties. According to the philosophy of Löwdin, to whom this volume is dedicated, the uncorrelated reference state for response properties ought to be taken as the unperturbed Hartree-Fock state for properties of all orders in the applied field. Frequently, however, it is operationally convenient to use the coupled Hartree-Fock like results as a standard of comparison for second- and higher-order properties, even though this is not consistent with Löwdin's choice for the uncorrelated reference state. In this method the reference state is the perturbed Hartree-Fock state. Numerical examples demonstrate a rather large difference between the two uncorrelated references. We consider the pros and cons of each choice.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 89 (1994), S. 375-382 
    ISSN: 1432-2234
    Keywords: Polarization propagator ; Dipole oscillator strength distribution ; Mean excitation energy ; Hydrogen ; Isotopes ; Temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The calculation of the effects of temperature and isotopic composition on the energy weighted moments of the dipole oscillator strength distribution of H2 in the random phase approximation to the polarization propagator are reported. It is seen that the effect of isotopic composition is small, while that of temperature is of an order accessible to experiment. We find that all the mean excitation energiesI μ, for μ=−1, 0, 1, decrease with temperature as does the dipole oscillator strength momentS(μ) for μ〉0, while the opposite is true for μ〈0. These effects are interpreted in terms of the bond length dependence of the excitation energies.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 371-386 
    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: We propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second-order polarization propagator approximation (SOPPA) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin-spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 283-297 
    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: We present early results from the CHANNEL code, which simulates the passage of ionized projectiles through bulk solids. CHANNEL solves the classical equations of motion for the projectile using a force obtained from the gradient of the quantum mechanically derived coulombic potential of the solid [determined via a full potential augmented plane wave (FLAPW) calculation on the bulk] and a quantum mechanical energy dissipation term, the stopping power, as determined from the method of Echenique, Nieminen, and Ritchie. The code then generates the trajectory of the ionic projectile for a given incident position on the unit cell face and an initial velocity. We use CHANNEL to generate an ion (proton) implantation profile for the test case of simple cubic hydrogen with the projectile's initial velocity parallel to the 〈100〉 channel. Further preliminary results for ion implantation profiles of protons in diamond structured Si, with initial velocity along the 〈100〉 and 〈110〉 channels, are given. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 299-308 
    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: We present the effects of structure, chemical binding, and number of layers on stopping for clean, unreconstructed diamond (100) one- to four-layer films with lattice constants fixed at crystalline values, and for graphite mono- and dilayers at their optimized bond lengths. First Born approximation stopping cross sections for protons incident normally on the films were obtained from orbital versions of the kinetic theory of stopping and of the local plasma approximation. The required electron momentum density was generated from the real space Kohn-Sham orbitals. We find a strong static quantum size effect in the stopping of diamond ultra-thin films as opposed to graphite, for which the stopping is only very weakly dependent on the layer number. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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