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  • 11
    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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  • 12
    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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  • 13
    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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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 561-570 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Advances in magnet construction technology have made magnets available with continuous fields of nearly 50 T and with bores of sufficient diameter for experiments. In addition to these magnets, already in use at the National High Magnetic Field Laboratory (NHMFL), semicontinuous pulsed sources of 100 T are anticipated in the near future. At its Los Alamos campus, the NHMFL has detonated pulsed magnets of over 1000 T. It thus becomes possible to investigate the behavior of molecules in strong fields with an eye to field-induced changes in such quantities as geometrical and electronic properties, spectroscopic properties, and reactivities. Theory is a useful probe for these quantities and serves to screen among possible candidates for experiments. In this contribution, we report preliminary results on the calculation of electronic properties of H2+, H2, and LiH, the simplest of molecules. Initial indications are that for increasing applied field strength, molecular bond lengths decrease and binding energies increase, with a concomitant increase in vibrational frequencies. Field-induced changes in these quantities, as well as in ground-state molecular potential energy surfaces are discussed, and suggestions are made for further investigations, both theoretical and experimental.    © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 561-570, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 15
    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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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 153-159 
    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 stopping of energetic ions by ultrathin films is of interest, as such films are mesoscopic structures which comprise the delamination limit of crystals, and as they are of practical interest because of their connection to microelectronics. A matter of special interest is the effect of the number of target layers on the stopping. Here we show that the stopping cross-section, S(N, v), of a system of N layers for projectiles with velocity v is a linear function of N-1 for small N. Such behavior would be expected for N → ∞, in which case the constant term would be the bulk crystalline cross section at the specified projectile velocity and the coefficient of the linear term would be the lowest-order surface correction. Surprisingly, the constant coefficient from a small N fit is reasonably consistent (within limits of imprecision) with the crystalline cross section. This linear scaling of S with N-1 for small N tracks the scaling behavior of the cohesive energy of the films. We discuss the physics and provide some illustrations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 17
    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
    Description / Table of Contents: On a examiné l'application de la méthode de Pariser-Parr-Pople aux systèmes avec des liaisons d'hydrogène. La courbe de potentiel pour le mouvement du proton a été calculée. La validité des résultats obtenus a été discutée.
    Abstract: Es wurde die Anwendung der Pariser-Parr-Pople Methode auf Systemen mit Wasserstoffbrücken untersucht. Die Potentialkurven für die Bewegung des Protons wurde berechnet und die Zuverlüssigkeit der erhaltenen Resultate diskutiert.
    Notes: In this work, the application of the Pariser-Parr-Pople scheme to hydrogen-bonded systems containing π electrons has been examined. The potential energy curves for the movement of the hydrogen atom in the bond have been calculated, and the reliability of the results obtained from this method, applied in this manner, have been discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 273-275 
    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 report here a summary of a limited CI calculation carried out on the C∞v and D∞h electronically excited states of bifluoride ion. This species is interesting as the prototype of a hydrogen-bonded system. It is determined that the lowest-lying excited states of the system are dissociative and/or autoionizing.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 1489-1489 
    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
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  • 20
    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
    Description / Table of Contents: Dans le premier article de cette série de publications sur la liaison d'hydrogène dans quelques systèmes simples avec des électrons π on a traité le complexe pyridine-pyridinium avec la méthode de Pariser-Parr-Pople. Dans le présent article on décrit un calcul semblable du système pyridine-pyrrole, ce qui permet une comparaison entre les résultats théoriques et des données experimentales.
    Abstract: In dem ersten Aufsatz dieser Reihe von Veröffentlichungen über Wasserstoffbrücken in einfachen Systemen mit π-Elektronen wurde der ideale Pyridin-Pyridiniumkomplex mit der Pariser-Parr-Pople-Methode behandelt. In diesem Aufsatz wird eine ähnlicke Berechnung des Pyridin-Pyrrolsystems beschrieben, was eine Vergleichung der theoretischen Resultate mit Experimentellen Tatsachen erlaubt.
    Notes: Previous work in this laboratory concerning the properties of hydrogen bonds in the base pairs of DNA [1-6] has led to considerable interest in the properties of hydrogen bonds in π-electron systems. The first paper in this series [7] has investigated the usefulness of the LCAO-MO-SCF method and the Pariser-Parr-Pople approximation as applied to this problem, by calculation on the ideal pyridine-pyridinium complex. In this paper, a relation with experiment will be established by comparison of the results obtained from this method of calculation with the properties of the experimentally observable pyridine-pyrrol system.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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