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  • 1
    Electronic Resource
    Electronic Resource
    Complete basis set extrapolation limit for electronic structure calculations: Energetic and nonenergetic properties of HeBr and HeBr2 van der Waals dimers (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 10438-10449 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The lowest 2Σ+ and 2Π electronic states of the HeBr molecule have been calculated by the ab initio coupled cluster approach in conjunction with a series of increasing size augmented correlation-consistent basis sets of double through quintuple zeta quality. Different extrapolation formulas to the complete basis set limit have been tested by comparing estimated and actual quintuple zeta quality counterpoise corrected interaction energies. Frozen-core approach is checked by performing calculations in which all electrons are correlated. The potential energy surfaces of the HeBr2 van der Waals complex have been obtained from the HeBr potentials by means of the diatomic-in-molecule approach. Finally, transport, scattering, and spectroscopic properties of HeBr and HeBr2(B) systems derived from ab initio data for different basis sets are examined. It is shown that their convergence closely follows the convergence of corresponding potential energy surfaces. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415078
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  • 2
    Electronic Resource
    Electronic Resource
    Periodic Hartree–Fock study of the adsorption of molecular oxygen on a reduced TiO2 (110) surface (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4798-4810 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical analysis of O2 adsorption on a reduced TiO2 (110) rutile surface, based on periodic ab initio Hartree–Fock calculations. Three different orientational approaches, three different spin symmetries, and two different adsorption sites are considered. We also consider the possibility that the surface can absorb more than one oxygen molecule. Positions of the surface ions, oxygen ions belonging to the third and fourth layers of the slab, and the bond lengths of the O2 and O2-substrate distances are optimized. Adsorption energies, admolecule-substrate bond lengths, spin densities and Mulliken charges are analyzed. The model is tested by comparing spin densities and relaxation parameters obtained for the reduced TiO2 (110) system to previous theoretical results. Finally, we discuss the relationship of our results to experimental observations of thermal desorption rates at low temperatures (100–600 K). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1394203
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  • 3
    Electronic Resource
    Electronic Resource
    Stability and structure of rare-gas ionic clusters using density functional methods: A study of helium clustersThis is a contribution to a symposium on “The Quantum Theory and the Chemical Bond” published in honor of Professor Roy McWeeney. The authors wish to affectionately dedicate this work to a great scientist and a long-standing friend. (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 593-608 
    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: Several modelings of exchange and correlation forces which can be carried out using density functional theory (DFT) methods have been analyzed to study their efficiency and reliability when evaluating possible competing structures of helium ionic clusters of increasing size. This study examines Hen+systems with n from 1 to 7 and compares the present calculations with earlier evaluations that used more conventional, and more computationally intensive, methods with configuration interaction (CI) approaches. The present results indicate that it is indeed possible to strike a fruitful balance between reduction of computational times and quality of the ensuing structural information. © 1996 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Relevant space within the spin-adapted reduced Hamiltonian theory. I. Study of the BH molecule (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 97-105 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The algorithm for evaluating the elements of the spin-adapted reduced Hamiltonian (2-SRH) involves the whole basis set of molecular orbitals. However, under a specific condition, its eigenvectors are very sparse. These two properties lead us here to propose a projection of the 2-SRH matrix, which is equivalent to an effective truncation which facilitates considerably the applicability of the SRH method. The criteria for performing this truncation, amounting to the determination of a relevant space are discussed. The results obtained for the BH molecule are analyzed here.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 97-105, 1997
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Relevant space within the spin-adapted reduced Hamiltonian theory. II. Study of the π cloud in benzene and naphthalene (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 107-119 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties of the spin-adapted reduced Hamiltonian (SRH) matrices and of their eigenvectors permit in many cases a projection of the two-electron matrices, which amounts to an effective truncation of the basis at the stage of the calculations which are time and as memory consuming. Besides this effective truncation of the basis, another simplification can be introduced by segregating an n-electron cloud from the N electrons of the system. Thus, the energy and the electron distribution of a smaller electronic cloud, for instance, the π or the σ cloud in aromatic systems, can be calculated; their separability being subsequently analyzed. Different relevant spaces have been examined in the study of the π-electron cloud in benzene and naphthalene.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 107-119, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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