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  • 101
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1829-1834 
    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 allylic rearrangement of trans-pinocarveol esters (I) to myrtenol esters (II), a reaction of interest in the chemistry of terpenes and cannabinoids, has been theoretically investigated. The intramolecular, cyclization-induced rearrangement results in equilibrium mixtures of the starting compounds and the products with the ratio of I vs. II in the equilibrium mixture being determined by their thermodynamic stabilities. The relative thermodynamic stabilities as reflected by calculated AM1 heats of formations (ΔHf) were determined for various I-II ester pairs. The study, in agreement with available experimental evidence, indicates that generally I, which contain an endocyclic double bond, are more stable and thus predominantly form following rearrangements. In two cases (acetate and pivalate) the stability is reversed. Calculations performed for similar structures, esters of 2-methylene cyclohexane-1-ol (IV) and 1-cyclohexene-1-methanol (V) gave similar results. Structural and electronic factors which might influence the stability of these compounds were examined. Interestingly, a correlation between thermodynamic stability and dipole moments was observed. © 1996 John Wiley & Sons, Inc.
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  • 102
    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 work, we evaluated structural and electronic similarities between a new class of acylhydrazones, recently presented as effective inhibitors of a Plasmodium falciparum cysteine protease, and a series of pyrazole arylacylhydrazones with analgesic and antiaggregating (antithrombotic) properties, using AM1. The calculated results suggest that at least one of the pyrazole compounds is similar enough to the active compounds to be considered as a candidate for a future antimalarial series. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996) 
    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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  • 104
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. v 
    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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  • 105
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1845-1849 
    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 integrated molecular transform, FTm, is a unitary structure index that has been successfully used for the correlation of two- and three-dimensional structure representations with their physicochemical and pharmacological properties; it has also been shown to be a unique conformational descriptor. In the present instance correlation trials were undertaken by regressing reported molecular skin permeability values on their respective calculated three-dimensional FTm indices. The index functioned not only as a structure descriptor but as a natural delineator in the series, separating several outliers in the data set and showing that excellent correlations may be obtained within the classical divisions of chemical structure. These results not only provide a means of estimating skin permeability directly from structure but also may have theoretical implications for studies of the nature and mechanism of dermal transport. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 106
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1851-1863 
    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: Using the information on the interatomic separations in a molecule, one can construct structural invariants that are the components of a molecular profile. The entries in the profile are derived by averaging different powers of the interatomic separations, suitably normalized so that the increasing powers do not dominate the sequence. Although only a few hundreds of structures have been so analyzed, no two different chemical structures were found to be characterized by the same sequences. A critical test for the conjecture that molecular profiles are unique is to consider structurally closely related systems that are very similar and have several similar properties. In this contribution we investigated the cuboctahedron and the accompanying polyhedron obtained by rotating half of the cuboctahedron against the other half, resulting in the so-called twist cutoctahedron. We show that even this pair of closely related structures has different profiles. We have also examined the generalized molecular profiles obtained by inserting n additional points along each edge of the polyhedra. The convergence of the profiles as n increases is discussed. It appears thus that these generalized molecular profiles, called line profiles or bond profiles, are likely to lead to a unique characterization of structures in which not only the geometry of atoms is recorded but also the geometry of the connectivity of the structure. © 1996 John Wiley & Sons, Inc.
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  • 107
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    International Journal of Quantum Chemistry 60 (1996), S. 1725-1725 
    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
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  • 108
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 199-205 
    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: This study demonstrates the use of uneven atomic basis sets for ab initio calculations of NMR shielding in the localized orbital/local origin (LORG) approach with norbornenone as the test case. We distinguish between locally dense sets (extended basis on target atom only) and locally saturated sets (extended bases on target atom and atoms in its first bonding sphere), using 6-311G** and 6-31G sets to describe the high and low level of function sets. It is shown that the use of these uneven sets can simulate high basis set level calculations of shieldings for 1H and for all the 13C nuclei in this molecule and, hence, allows quite accurate ab initio calculations of shielding properties of these nuclei in large molecules using relatively modest computational facilities. The shielding of the double-bonded 17O nucleus is apparently sensitive to basis-set quality beyond the first bonding sphere. © 1996 John Wiley & Sons, Inc.
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  • 109
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    International Journal of Quantum Chemistry 57 (1996), S. 207-212 
    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: Bond function basis sets combined with the counterpoise procedure are used to calculate the molecular dissociation energies De of 24 diatomic molecules and ions. The calculated values of De are compared to those without bond functions and/or counterpoise corrections. The equilibrium bond lengths re and harmonic frequencies οe are also calculated for a few selected molecules. The calculations at the fourth-order Møller-Plesset approximation (MP4) have consistently recovered about 95-99% of the experimental values for De; compared to as low as 75% without use of bond functions. The calculated values of re are typically 0.01 Å larger than the experimental values, and the calculated values of οe are over 95% of the experimental values. © 1996 John Wiley & Sons, Inc.
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  • 110
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    International Journal of Quantum Chemistry 57 (1996), S. 235-243 
    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 diagonalization of a class of lattice spin models of a particular structure is first reviewed and secular polynomials for these models are calculated explicitly from the corresponding secular matrices. The structure of the eigenvectors of the given secular matrices is investigated and used to determine the eigenvalues theoretically, and proofs which have not appeared are presented. These results can be compared to the results obtained from the full secular polynomials. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
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  • 111
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    International Journal of Quantum Chemistry 57 (1996), S. 501-518 
    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 recently proposed pair population scheme is investigated for ab initio SCF and spin-coupled wave functions. All the required expressions are rederived, in very compact form, and efficient computational schemes are presented for their evaluation. As representative examples of different types of bonding, pair populations and related quantities are examined for H2, LiH, BeH, CH4, H2O, and B2H6. Various “effective valencies” are also considered. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 112
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996) 
    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
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  • 113
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    International Journal of Quantum Chemistry 57 (1996), S. 567-573 
    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 study of the coronene - coronene association using different interaction potentials based on an atom-atom pair potential proposed by Fraga has been performed. The interaction potentials employed differ in the way the electrostatic and/or dispersion contributions are computed. The influence of both contributions on the geometries predicted for the coronene dimer is discussed in order to analyze the effectiveness of the different interaction potentials. The stationary points found in each interaction energy hypersurface are characterized by calculating the Hessian eigenvalues. Results are discussed in the light of those previously reported for the benzene dimer. Stacked-displaced structures are suggested to be the preferred conformations for the coronene - coronene association. © 1996 John Wiley & Sons, Inc.
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  • 114
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    International Journal of Quantum Chemistry 57 (1996), S. 575-585 
    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: Spectroscopic properties of all the electronic states of KRb dissociating into 4s(K) + 5s(Rb), 4s(K) + 5p(Rb), 4p(K) + 5s(Rb), and 4s(K) + 4d(Rb) and some higher-lying excited states are studied with ab initio calculations. Spectroscopic constants, dipole moments, and the nature of the electronic wave functions for these states are reported. Intensities for the singlet-singlet and triplet-triplet transitions are theoretically calculated from the potential energy curves and the transition dipole moments. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 115
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    International Journal of Quantum Chemistry 57 (1996), S. 587-594 
    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 outer-valence ionization potentials, low-lying electronically excited states, and 1J(CC) nuclear spin-spin coupling constants of bicyclobutane, tricyclopentane, tricyclohexane, and octabisvalene have been investigated at the ab initio level by using the outer-valence Green function (OVGF), random-phase approximation (RPA), and equations-of-motions (EOM) approaches, which incorporate the main dynamical correlation effects. A comprehensive theoretical prediction of these spectroscopic observables is presented, which shows several interesting aspects stemming from the unique electronic structure of the bridge bond. © 1996 John Wiley & Sons, Inc.
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  • 116
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    International Journal of Quantum Chemistry 57 (1996), S. 611-623 
    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 full theoretical treatment of electron capture processes using ab initio configuration interaction methods within, according to the collision energy range concerned, a semiclassical or a quantal collisional formalism including translation effects has been developed recently. An application for collisions involving boron, an important impurity in fusion reactors, is presented on examples of the ground state: B3+(1s2) + He, B4+(1s) + H, and the metastable ion B3+(1s2s) + H reactions. © 1996 John Wiley & Sons, Inc.
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  • 117
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    International Journal of Quantum Chemistry 57 (1996), S. 7-15 
    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 solution of the Schrödinger equation for the d-dimensional hydrogen atom in a d-dependent potential defined by Gauss' law has been studied by the shifted 1/d method and the δ expansion. These methods provide analytical formulas for the eigenvalues and eigenfunctions which have been tested against “exact” numerical values obtained recently. The comparison shows that the results obtained with the analytical expressions are in excellent accord with the numerical ones and, on the other hand, provide a theoretical justification for a proposed empirical expression for the energies of the two-dimensional hydrogen atom with a logarithmic potential energy function. © 1996 John Wiley & Sons, Inc.
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  • 118
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    International Journal of Quantum Chemistry 57 (1996), S. 43-51 
    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: Analytical exact expressions are obtained for matrix elements of the modified Pöschl-Teller oscillator over different operators including powers of the hyperbolic functions sinh(α x), cosh(α x), and tanh(α x) and the differential operators d/dx and d2/dx2. These expressions are derived using explicitly the Pöschl-Teller eigenfunctions. In addition, several recursion relations connecting different Pöschl-Teller matrix elements are obtained using the factorization and hypervirial techniques. It is shown that these relations can be used to make easier the computation of the matrix elements. © 1996 John Wiley & Sons, Inc.
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  • 119
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    International Journal of Quantum Chemistry 57 (1996), S. 105-111 
    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 chemisorption of atomic hydrogen and oxygen on a cobalt surface has been studied on a five-atom cluster model using one-electron effective core potential (1e-ECP) and all-electron calculations at the ab initio SCF and MCPF levels. Also, density functional calculations have been carried out. The different approaches are evaluated. The 1e-ECP has been compared to similar ECPS for nickel and copper. Our results indicate that this approach is valid also for cobalt. Different contributions to the cluster-adsorbate bonding energy are discussed. © 1996 John Wiley & Sons, Inc.
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  • 120
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    International Journal of Quantum Chemistry 57 (1996), S. 1-2 
    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
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  • 121
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    International Journal of Quantum Chemistry 58 (1996) 
    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
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  • 122
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    International Journal of Quantum Chemistry 58 (1996), S. 539-540 
    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
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  • 123
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    International Journal of Quantum Chemistry 58 (1996), S. 537-537 
    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
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  • 124
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    International Journal of Quantum Chemistry 59 (1996), S. 3-6 
    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: Irregularities in the connection of the high- and low-density forms of the Perdew-Zunger correlation energy functional lead to computational difficulties that are removed by a new parametrization. These parametrizations and a number of other correlation functionals are compared and discussed. © 1996 John Wiley & Sons, Inc.
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  • 125
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    International Journal of Quantum Chemistry 59 (1996), S. 15-29 
    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 general expression for the sixth-order Møller-Plesset (MP6) energy, E(MP6), has been dissected in the principal part A and the renormalization part R. Since R contains unlinked diagram contributions, which are canceled by corresponding terms of the principal part A, E(MP6) has been derived solely from the linked diagram terms of the principal part A. These have been identified by a simple procedure that starts by separating A into connected and disconnected cluster operator diagrams and adding terms associated with the former fully to the correlation energy. After closing all open disconnected cluster operator diagrams, one can again distinguish between connected and disconnected energy diagrams, of which only the former lead to linked diagram representations and, therefore, contributions to E(MP6). The connected diagram parts of A have been collected in four energy terms E(MP6)1, E(MP6)2, E(MP6)3, and E(MP6)4. The sum of these terms has led to an appropriate energy formula for E(MP6) in terms of first- and second-order cluster operators. © 1996 John Wiley & Sons, Inc.
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  • 126
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    International Journal of Quantum Chemistry 59 (1996), S. 71-95 
    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: Three different ways of getting reliable estimates of full configuration interaction (FCI) correlation energies are tested, namely (a) by Padé approximants [k, k] and [k, k - 1], (b) by using extrapolation formulas, and (c) by Feenberg scaling of Møller-Plesset (MP) correlation energies. By using MPn energies up to sixth order, i.e., MP2, MP3, MP4, MP5, and MP6, it was possible to test the convergence behavior of the Padé series [1, 0], [1, 1], [2, 1], [2, 2] and the Feenberg series up to sixth order where in the latter case a scaling factor λ(5) (scaling of the second-order wave function, FE2) rather than the previously tested λ(3) (scaling of the first-order wave function, FE1) was considered. Investigation of 26 different correlation energies for systems with monotonic convergence in the MPn series (class A systems) or initially oscillatory convergence behavior (class B systems) indicates that Padé approximants lead in some cases to reasonable estimates of FCI correlation energies, but in other cases, in particular for class B systems, they give too negative correlation energies. Both monotonic and oscillatory behavior for the Padé series is observed where it is possible to predict its convergence behavior on the basis of calculated MPn energies. The best estimates of the FCI correlation energy are obtained by FE2 scaling. At sixth-order FE2, values for atoms and molecules with equilibrium geometry differ on the average by just 0.146 mhartree from FCI correlation energies. The FE2 correlation energies all converge monotonicly. Also, FE2 scaling reduces the exaggeration of MP6 correlation energies for class B systems. However, surprisingly good estimates of FCI energies are also obtained by simple extrapolation formulas based on MP4, MP5, and MP6 correlation energies. © 1996 John Wiley & Sons, Inc.
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  • 127
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    International Journal of Quantum Chemistry 59 (1996), S. 97-102 
    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 characteristic polynomial associated with π-electrons of conjugated molecules are discussed by using subgraphs derived from molecular graphs as a basis for their construction. A practical method has been developed for evaluating the coefficient aK of conjugated molecules. Applying this method, the general formulas of evaluating the coefficient aK for homologous conjugated molecules have been obtained. The approach is illustrated on a few simple conjugated systems, including also a few polymeric systems. © 1996 John Wiley & Sons, Inc.
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  • 128
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    International Journal of Quantum Chemistry 59 (1996), S. 103-108 
    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: Calculations are reported of X3zz,zz,z,z(-iω;iω,0,0), X3zz,zz,x,x(-iω;iω,0,0), X3zzz,z,z,z(-iω;iω,0,0), X4zz,z,z,z,z(-iω;iω,0,0,0), and X4zz,x,x,z,z(-iω;iω,0,0,0) for H and He. These are the independent components of the atomic (quadrupole)2-(dipole)2, (octupole)-(dipole)3, and (quadrupole)-(dipole)4 hyperpolarizability tensors for an imaginary frequency iω. The first three quantities have been used for the determination of the R-8 dispersion contribution to the H-H, H-He, and He-He collision-induced pair polarizability functions. The last two quantities will be needed in future calculations of the leading order (R-7) dispersion contributions to the collision-induced first hyperpolarizability (β) for the H-He pair. The calculations were based on sum-over-states formulations with near-exact wave functions for H and highly accurate explicitly electron-correlated wave functions for He. For this reason we believe them to be of benchmark quality. © 1996 John Wiley & Sons, Inc.
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  • 129
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    International Journal of Quantum Chemistry 59 (1996), S. 109-117 
    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 local grid method proposed earlier is used to model chemical dynamical events in more than one dimension. Two different mean-field routes are applied to model problems representing dynamics of isomerization, H+-ion transfer, energy transfer, etc. The methods are seen to work with equal facility for both time-dependent and time-independent potentials. © 1996 John Wiley & Sons, Inc.
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  • 130
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    International Journal of Quantum Chemistry 57 (1996) 
    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
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  • 131
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    International Journal of Quantum Chemistry 57 (1996), S. 811-821 
    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: Ab initio dynamic polarizabilities per unit cell of infinite stereoregular molecular hydrogen chains are calculated at the coupled Hartree-Fock level of approximation by using the random-phase approximation and the STO-3G and double-zeta atomic basis sets. Comparison with molecular calculations on increasingly large oligomeric chains emphasizes the nice extrapolation property of the polymeric technique that provides asymptotic values very close to the largest oligomeric values. The poles of the polarization propagator associated with the electric dipole polarizability correspond to the singlet excitation energies. Comparisons are performed with other techniques that provide the band gap. © 1996 John Wiley & Sons, Inc.
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  • 132
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    International Journal of Quantum Chemistry 57 (1996), S. 823-841 
    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 results of detailed theoretical investigations of the properties of atomic and diatomic H in GaAs were analyzed with the effort to give a unified picture of the H behavior in this semiconductor. All calculations were performed in the pseudopotential density-functional framework using a supercell approach. We studied both shallow impurities (Si and C) and deep point defects (As antisite and Ga vacancy). Generally, a simple scheme may be applied in order to describe the H interaction with shallow impurities, where a key role is played by the amphoteric character of H. More complex mechanisms are involved in the deep impurity case that are related to new, interesting effects of H incorporation in GaAs. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 57 (1996), S. 843-849 
    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 electrostatic potential and the intensity of the electric field above the isolated layer of the phyllosilicate mineral talc (layer group symmetry C2/m) were computed using the semiempirical INDO/2 method. The electrostatic potential Vc and the intensity of electric field (OVERBAR)Ec, above the surface of semi-infinite crystal were obtained as the sum of the contributions of the infinite number of individual layers. The interaction energy Uint between a noble gas atom and the talc crystal was computed as (a) a pure Lennard-Jones energy ULJ and (b) the sum of ULJ and interaction energy with induced dipole moment: Uind = α|(OVERBAR)E|2, where α is the dipole polarizability of the noble gas atom. The one-particle configurational integral was calculated within the classical mechanics limit. Both the free and adsorbed gas phases were assumed to be ideal. The obtained results demonstrate that in the case of uncharged and nonpolar adsorbate and an uncharged surface the electrostatic part of the interaction energy should be included in the total interaction energy. © 1996 John Wiley & Sons, Inc.
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  • 134
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    International Journal of Quantum Chemistry 57 (1996), S. 851-860 
    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: Ab initio crystal orbital calculations on three-dimensional crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ), diprotonated deoxycytidine-5′-monophosphate monohydrate (5′-dCMP*2H*1Water), disodium deoxyguanosine-5′-monophosphate tetrahydrate (5′-dGMP*2Na*4Water), disodium uridine-3′-monophosphate tetrahydrate (3′-UMP*2Na*4Water), monosodium monoprotonated deoxyadenosine-5′-monophosphate hexahydrate (5′-dAMP*1H*1Na*6Water), disodium deoxycytidine-5′-monophosphate heptahydrate (5′-dCMP*2Na*7Water), cis-polyacetylene (cis-PA), and polythiophene (PTP) were carried out using the CRYSTAL92 routine package. A suitable basis set has been found that enables one to carry out the above calculations at the STO-3G level of accuracy using SILICON GRAPHICS workstations. However, to obtain reasonable results for three-dimensional crystals of polymers, one has to use much more extended basis sets. © 1996 John Wiley & Sons, Inc.
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  • 135
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    International Journal of Quantum Chemistry 59 (1996), S. 147-165 
    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 problem of excitons in interaction with phonons in a molecular crystal has been reinvestigated as a continuation of our earlier work. The exciton-phonon interaction has been taken to be linear in lattice displacements. The external medium, the phonon assembly, has been considered to be in thermal equilibrium. Following Simons, we have incorporated the effects of the medium on the exciton dynamics into a time-dependent effective potential that contains the equilibrium average exciton-phonon interaction as well as terms arising from the fluctuations in the medium's coordinates about their equilibrium values. A correlation function that represents the probability of exciton transfer has been given in the interaction picture. The time evolution of this correlation function has been determined by following Kubo's technique of cumulant expansion. The zeroth-, second-, and fourth-order contributions to the correlation function have been calculated in this way. The second- and fourth-order contributions have been diagrammatically represented. The second-order contribution has been explicitly calculated in different physical limits, namely, the slow exciton and the slow phonon limits at high and low temperatures and for very large and very small time. A few simple formulas for the transfer probability of a bare exciton in a molecular crystal of cubic symmetry have been derived from the Debye approximation for the dispersion of phonons. It has been specifically shown that the sum over phonon modes in the large time dynamics leads to a fully destructive interference in second order at a very low temperature and gives rise to a diffusive transport at a high enough temperature. A natural way of clothing the excitons has been considered and the clothed exciton has been represented diagrammatically. The dressing requires the correlation function to be redefined in terms of the clothed states and the clothed operators. The clothed exciton correlation function that represents the probability of transfer of excitons fully clothed by the phonons in thermal equilibrium turns out to be identical with the bare exciton correlation function. This attaches a novel interpretation to the correlation function which was originally defined by Simons. Transfer probabilities for a clothed exciton in a cubic crystal has been explicitly worked out for different physical limits under the Debye model of phonon dispersion. From these results a few expressions for the macroscopic diffusion coefficient of the clothed exciton have been obtained. A few critical comments have been incorporated. © 1996 John Wiley & Sons, Inc.
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  • 136
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    International Journal of Quantum Chemistry 59 (1996), S. 173-182 
    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 simple formalism of real irreducible tensorial sets of real bases is proposed. The definition of the real bases, the coupling of the real bases, and the transformation of the real bases in a group chain including the three-dimensional rotation group and the molecular point groups are studied. The double coset technique is used to derive the close formulas for generating the coupling coefficients and the transformation coefficients. © 1996 John Wiley & Sons, Inc.
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  • 137
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    International Journal of Quantum Chemistry 57 (1996), S. 141-155 
    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 matrix differential calculus is applied for the first time to a quantum chemical problem via new matrix derivations of integral formulas and gradients for Hamiltonian matrix elements in a basis of correlated Gaussian functions. Requisite mathematical background material on Kronecker products, Hadamard products, the vec and vech operators, linear structures, and matrix differential calculus is presented. New matrix forms for the kinetic and potential energy operators are presented. Integrals for overlap, kinetic energy, and potential energy matrix elements are derived in matrix form using matrix calculus. The gradient of the energy functional with respect to the correlated Gaussian exponent matrices is derived. Burdensome summation notation is entirely replaced with a compact matrix notation that is both theoretically and computationally insightful. © 1996 John Wiley & Sons, Inc.
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  • 138
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    International Journal of Quantum Chemistry 57 (1996), S. 183-198 
    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 virial field V(r) is defined by the local statement of the quantum mechanical virial theorem, as the trace of the Schrödinger stress tensor. This field defines the electronic potential energy density of an electron at r and integrates to minus twice the electronic kinetic energy. It is the most short-ranged description possible of the local electronic potential energy and it exhibits the same transferable behavior over bounded regions of real space (corresponding to the functional groups of chemistry) as does ρ(r). This article establishes a structural homeomorphism between -V(r) and ρ(r), showing that the two fields are homeomorphic over all of the nuclear configuration space. The stable or unstable structure defined by the gradient vector field Δρ(r; X) for any configuration X of the nuclei can be placed in a one-to-one correspondence with a structure defined by the field -ΔV(r; X′). In particular, a molecular graph for ρ(r) defining a molecular structure is mirrored by a corresponding virial graph for V(r) and the lines of maximum density linking bonded nuclei in the former field are matched by a set of lines of maximally negative potential energy density in the latter. The homeomorphism is also geometrically faithful, an equilibrium geometry in general, exhibiting equivalent structures in the two fields. The demonstration that the virial field, whose integrated value equals twice the total energy, is essentially just a locally scaled version of the electron density is suggestive of possible new approaches in density functional theory. © 1996 John Wiley & Sons, Inc.
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  • 139
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    International Journal of Quantum Chemistry 57 (1996), S. 219-227 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the first hydrogen bond of the guanine-cytosine (G-C) pair, the potential function V(r, R) is found for the nonequilibrium bond length R. A new form of the semiempirical potential function, Clementi's calculations for V(r, R0) and some experimental data are used. New wave functions and energy levels as a function of the H-bond length for the ground and several excited states are obtained. This allows one to obtain frequencies and amplitudes of some vibrations of the G-C pair side groups involved in the formation of the hydrogen bond when the latter is not excited and when it is excited to the first energy level. © 1996 John Wiley & Sons, Inc.
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  • 140
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of a hydroxyl group simulating Ser-48 in the hydride-transfer step characteristic of liver alcohol dehydrogenase is studied on the hydride-transfer reaction as modeled by a methanolate anion interacting with a cyclo propenyl cation. It is shown first that this is an adequate model by comparing it to the methanolate-pyrydinium cation model transition structure, (TS). The side-chain effect is modeled first by adding water and then with methanol located at the position that Ser-48 occupies in the enzyme; a supermolecule approach is used. It is found that (i) the normalized advance coordinate (NAC) for the exchanged hydrogen has an invariant value at the TS and the reactant, while for the product, the NAC depends upon the external perturbation introduced by the ancillary molecule (the TS is reactant-like); (ii) the products are strongly destabilized, so the (activation) barrier with respect to the TS diminishes; (iii) the energy gap between reactants and products is sensibly diminished by the presence of methanol; (iv) the alcoholate moiety in the hydride transfer complex is not spontaneously protonated; and (v) there is a negligible charge transfer between the hydride-transfer system and models of Ser-48. In the present simplified model, methanol appears to have a catalytic effect via hydrogen bonding. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 57 (1996), S. 261-261 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 142
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    International Journal of Quantum Chemistry 57 (1996), S. 281-293 
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    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 how the regularized two-component relativistic Hamiltonians of Heully et al. and Chang, Pelissier, and Durand can be viewed as arising from a perturbation expansion that unlike the Pauli expansion remains regular even for singular attractive Coulomb potentials. The performance of these approximate Hamiltonians is tested in the framework of the local density approximation and the relation of their spectrum to that of the Dirac Hamiltonian is discussed. The circumstances under which the current approximations are superior to the Pauli Hamiltonian are analyzed. Finally, it shown how the Hamiltonians could be used within the context of conventional Hartree-Fock theory. © 1996 John Wiley & Sons, Inc.
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  • 143
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    International Journal of Quantum Chemistry 57 (1996), S. 321-325 
    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 sampling of the exact solution of the Schrödinger equation by quantum Monte Carlo methods allows one to solve the problem of the optimization of linear and nonlinear parameters of a trial wave function by minimization of the distance to the exact wave function in Hilbert space even for those systems whose exact wave function is unknown. The overlap integrals between the basis functions and the exact wave function can be easily estimated within the quantum Monte Carlo formalism. Several observables of the helium atom ground state, computed both within the orbital approximation and by an explicitly correlated basis set, evidence the overall goodness of the wave function optimized according to this criterion. © 1996 John Wiley & Sons, Inc.
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  • 144
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    International Journal of Quantum Chemistry 57 (1996), S. 871-879 
    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: Ab initio RHF/STO-3G, 3-21G, and 6-31G band structure calculations were carried out on an extended regular chain of beryllium atoms ((SINGLEBOND)Be2(SINGLEBOND))∞ to study its stability in comparison with corresponding data on finite chains and previously reported results on small elemental beryllium clusters. It is found that, starting from a linear distribution of atoms along the chain, the system evolves toward a regular zigzag planar structure. The total RHF energy per constituent atom is higher for the chains than for the clusters and is thereby suggestive of that isolated chains are unlikely to exist except in constraining channels of host structures. In the limit of the infinite chain, there are signs indicating that the RHF model is no longer an adequate description. © 1996 John Wiley & Sons, Inc.
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  • 145
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    International Journal of Quantum Chemistry 57 (1996), S. 881-886 
    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 assumption of the concentration dependence of the energy of formation of vacancy-type defects (VTD) in solids is applied to the procedure of the estimation of the defect interaction parameters. The VTD effective interaction is described by the mixing potential. The sign of this potential characterizes the stability of the VTD-atom “alloy.” Employing the example of Nb, we illustrate the ability of the suggested approach to describe the stability of the VTD-atom “alloy.” © 1996 John Wiley & Sons, Inc.
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  • 146
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    International Journal of Quantum Chemistry 57 (1996), S. 887-896 
    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: Extensive self-consistent real-space recursion-method calculations were performed for the Pt overlayer or the Pt7 cluster on the Ni(111) surface and for hydrogen chemisorption on these systems. Correlations between the surface-atom local density of electronic-state properties before chemisorption, surface reactivity, and the initial-state contribution to the metal core-level shifts, respectively, is documented and discussed. The experimentally observed catalytic properties of Pt—Ni alloy surfaces are also briefly considered. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 57 (1996), S. 897-901 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the basis of a nonempirical pair potential, the temperature dependencies of the long-range-order parameter of NiTi and AuPd are calculated. The suggested effective potential approach allows one to describe the changes in phase relations. The evaluation of the internal mixing energy of alloys is carried out in the framework of the static concentration waves theory of Khachaturyan. The model outlines the technique to calculate the values of the energy parameters of the ordering process from first principles. © 1996 John Wiley & Sons, Inc.
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  • 148
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    International Journal of Quantum Chemistry 57 (1996), S. 259-259 
    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
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  • 149
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    International Journal of Quantum Chemistry 57 (1996), S. 265-280 
    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: Sequence transformations, which transform a slowly convergent or divergent sequence {sn}∞n&=0 into a new sequence {sln}∞n=0 with hopefully better numerical properties, are useful computational tools to overcome convergence and divergence problems. In this article, sequence transformations are discussed that use explicit remainder estimates [E.J. Weniger, Comput. Phys. Rep. 10, 189 (1989)]. Because of the explicit incorporation of the information contained in the remainder estimates, these transformations are potentially very powerful and well suited for the summation of strongly divergent series. The Rayleigh-Schrödinger perturbation series for the ground-state energy of the quartic, sextic, and octic anharmonic oscillator is a typical example of a perturbation series that diverges quite strongly for every nonzero coupling constant. It can be summed efficiently even in the very challenging strong coupling regime, if sequence transformations are combined with a suitable renormalization technique described by F. Vinette and J. C˘íz˘ek [J. Math. Phys. 32, 3392 (1991)]. Moreover, a renormalized strong coupling expansion for the ground-state energy of an anharmonic oscillator can be constructed, which apparently converges for all coupling constants β ε [0,∞) and which makes the computation the ground-state energy almost trivial. Other applications of sequence transformations in quantum mechanical and quantum chemical calculations are also reviewed. © 1996 John Wiley & Sons, Inc.
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  • 150
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    International Journal of Quantum Chemistry 57 (1996), S. 309-319 
    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: Gradient corrections to the local spin density (LSD) approximation for the exchange-correlation energy are making density functional theory as useful in quantum chemistry as it is in solid-state physics. But which of the many gradient-corrected density functionals should be preferred a priori? We make a graphical comparison of the gradient dependencies of some popular approximations, discussing the exact formal conditions which each obeys and identifying which conditions seem most important. For the exchange energy, there is little formal or practical reason to choose among the Perdew-Wang 86, Becke 88, or Perdew-Wang 91 functionals. But, for the correlation energy, the best formal properties are displayed by the nonempirical PW91 correlation functional. Furthermore, the real-space foundation of PW91 yields an insight into the character of the gradient expansion which suggests that PW91 should work especially well for solids. Indeed, while improving dissociation energies over LSD, PW91 remains the most “local” of the gradient-corrected exchange-correlation functionals and, thus, the least likely to overcorrect the subtle errors of LSD for solids. To show that our analysis of spin-unpolarized functionals is sufficient, we also compute spin-polarization energies for atoms, finding PW91 values only slightly more negative than LSD values. © 1996 John Wiley & Sons, Inc.
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  • 151
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    International Journal of Quantum Chemistry 57 (1996), S. 453-463 
    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: An approach for a space-separated calculation of the wave function in the valence and core regions of a molecule is proposed. As the first step, the calculation of the orbitals (or two-component spinors in the relativistic case) in the valence region by the effective core potential (ECP) method is performed. Then, it is followed by a restoration of orbitals (four-component spinors) expanded on spherical harmonics in the core regions of heavy atoms. Theoretical questions of the variational calculation of the molecular orbitals are considered in some core region limited by a sphere. Inclusion from the electronic cloud outside this region is reduced by the necessity of taking into account the orthonormality and boundary conditions together with an effective external field in respect to the selected core region.This method may be used for calculation of matrix elements of operators that are singular near nuclei (P, T-odd interactions, hyperfine structure, etc.). A substantial computational saving can be reached because the method enables, by the most optimal way, to combine the advantages of two well-developed approaches: molecular ECP calculations in the Gaussian basis set and one-center numerical atomic calculations with an external field. It is especially important when the relativistic effects are taken into account. © 1996 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 57 (1996), S. 471-479 
    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: Four-component relativistic and nonrelativistic molecular orbital calculations were performed for the covalent paramagnetic complex [Ir(CN)5]3-, employing the self-consistent discrete variational method, in the framework of density functional theory. Relativistic effects on the electronic structure and chemical bonding are discussed by comparison of relativistic and nonrelativistic one-electron energy levels, populations, and bond orders. The influence of relativistic effects on calculated absorption energies of the electronic spectrum is briefly assessed. © 1996 John Wiley & Sons, Inc.
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  • 153
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    International Journal of Quantum Chemistry 57 (1996), S. 481-491 
    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: Insertion of CO2 into the transition metal-hydride bond of [RhIIIH2(PH3)3]+, CuIH(PH3)2, and RhIH(PH3)3 was theoretically investigated with ab initio MO/MP4, SD-CI, and CCD methods. The geometries of reactants, transition states (TS), and products were optimized at the Hartree-Fock level, and then MP4, SD-CI, and CCD calculations were performed on those optimized structures. The TS of the CO2 insertion into the CuI(bond)H bond is the most reactantlike, while the TS of the CO2 insertion into the RhIII(bond)H bond is the most productlike. The activation energy (Ea) and the reaction energy (ΔE) were calculated to be 6.5 and -33.5 kcal/mol for the CO2 insertion into the Cu1(bond)H bond, 21.2 and -7.0 kcal/mol for the CO2 insertion into the Rh1(bond)H bond, and 51.3 and -1.1 kcal/mol for the Rh111(bond)H bond at the SD-CI level, where negative ΔE represents exothermicity. These results are discussed in terms of the M(bond)H bond energy and the trans-influence of the hydride ligand. © 1996 John Wiley & Sons, Inc.
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  • 154
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    International Journal of Quantum Chemistry 57 (1996), S. 519-532 
    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: On the grounds of results from quantum chemical calculations, we introduce spin-catalysis as a new concept, and classify different types of chemical reactions according to this concept. We propose a general definition of spin-catalysis as phenomena in which chemical reactions are promoted by substances which assist in overcoming spin-prohibition or in which the activation barrier is lowered through spin uncoupling induced by a paramagnetic catalyst. A number of known phenomena fall into this definition and can be classified according to two main categories: (1) spin-orbit coupling induced and (2) paramagnetic-exchange induced spin-catalysis. Other types of spin-catalysis are also discussed: (3) processes with participation of substances which assist in (a) photochemical and (b) thermal or electrochemical generation of active particles by energy and - by electron transfer [radicals, diradicals, O2(1Δg), etc.], reacting further without spin-prohibition: (4) processes induced by an external magnetic field. Processes (3) and (4) are quite general and well known; their inclusion in the spin-catalysis classification does not introduce any new findings for the chemical kinetics, but the general features, which unite them with the important catalytic processes of the first two types, serve as a useful guide in catalysis theory. Few models of spin-catalytic processes have been simulated for the purpose of illuminating the principles of spin-catalysis; the cis-trans isomerization of ethylene catalyzed by molecular oxygen, the external heavy atom effect in ethylene photochemistry, and some others. © 1996 John Wiley & Sons, Inc.
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  • 155
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    International Journal of Quantum Chemistry 57 (1996), S. 533-542 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The performance of numerical basis sets in relation to Gaussian basis sets is examined, by studying 20 small sulfur-containing molecules. The results of geometry optimization calculations are reported for each molecule using both density functional and Hartee-Fock methods. In comparison with experimental data, it is shown that the use of numerical bases tend to overestimate structural parameters, particularly bond lengths, and, in most cases, more than Gaussian basis sets. It is also shown that the use of a larger Gaussian basis set in DFT calculations has the effect of reducing bond lengths. © 1996 John Wiley & Sons, Inc.
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  • 156
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    International Journal of Quantum Chemistry 57 (1996), S. 663-671 
    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: Many of the important properties of transition-metal complexes depend on the low-energy excitation spectrum formed by d-electrons of the central transition-metal atom. The spectra of this type are usually fit to the well-known crystal field theory or to the angular overlap model. The result of the fitting is a set of parameters which are considered as characteristics of the electronic structure of the complex such as strength of the ligand field or types and extent of metal-ligand bonding. We present here a short account of the effective Hamiltonian method recently developed to calculate the splitting of the d-levels by the ligands and the resulting d-d spectra of transition-metal complexes together with some results of its application to the mixed-ligand complexes with the general formula ML4Z2, where M = V, Co, Ni; L = H2O, NH3, Py; and Z = H2O, NCS-,C -l. Particular attention is paid to the V(H2O)4Cl2 and Co(H2O)4Cl2 compounds. The former seems to have tetragonal structure, whereas for the latter, our method predicts a spatially degenerate ground state for the tetragonal arrangement of the ligands. That must lead to the Jahn-Teller distortion, which is actually observed. © 1996 John Wiley & Sons, Inc.
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  • 157
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    International Journal of Quantum Chemistry 57 (1996), S. 697-705 
    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 results of ab initio RHF/3-21G, RHF/6-31G*, and MP2/6-31G** / / HF/6-31G* calculations for 10 possible configurations of OM4H6 molecules (MO · 3MH2, M = Be, Mg) are reported. Five isomers of OBe4H6 and three isomers of OMg4H6 have been found within an energy range of ã 15 kcal mol-1. The “lanternlike” C3v structure is the most favorable one for both complexes. Both molecules OM4H6 are stable to decomposition through all of the studied pathways. Chemical bonding in the OMk polyhedra containing two-, three-and four-coordinated oxygen atoms is discussed. © 1996 John Wiley & Sons, Inc.
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  • 158
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    International Journal of Quantum Chemistry 57 (1996), S. 721-728 
    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: Three stable tautomeric forms, dienol (DE), ketoenol (KE), and diketo (DK), of 2,2′-bipyridyl-3,3′-diol BP(OH)2 were found in this study, using the semiempirical AM1 and MNDO-PM3 and ab initio (4-31G basis set) methods. All calculations were carried out without any symmetry restrictions. There is a good agreement between the ab initio calculated and experimentally obtained structural parameters for the DE tautomer. Transition structures, corresponding to the DK → KE and KE → DE processes have also been found. On the basis of the results from the present work, an asynchronous (two-step) DK → KE → DE mechanism of the IPT reaction in BP(OH)2 is proposed. © 1996 John Wiley & Sons, Inc.
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  • 159
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    International Journal of Quantum Chemistry 57 (1996), S. 715-719 
    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 reaction mechanism of the α, α and α, β elimination of hydrogen fluorides from alkyl fluorides has been studied theoretically. For fluoroethane as a reactant, the transition state (TS) optimized at the level of the 6-31G** basis set shows that the α, β elimination proceeds via a four membered-ring TS with a barrier height 64.6 kcal/mol, while the α, α elimination, via a three-membered ring TS with a 83.7 kcal/mol barrier. Four substituents, CH3, CN, F, and NH2, were used to investigate the substituent effect of elimination by using the 3-21G basis set. The calculated barriers show that NH2-substituted alkyl fluorides favor both the α, α and α, β elimination and these two reactions would be expected to proceed simultaneously. © 1996 John Wiley & Sons, Inc.
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  • 160
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    International Journal of Quantum Chemistry 57 (1996), S. 729-733 
    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: Ab initio calculations were performed on the N-methylpyridones lithiated on the aromatic ring using a 6-31G* basis set. Whenever the lithium atom is on a carbon adjacent to the carbonylic group, a bridged structure is obtained where lithium is coordinated to both carbon and oxygen; these structures are the most stable isomers. © 1996 John Wiley & Sons, Inc.
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  • 161
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    International Journal of Quantum Chemistry 57 (1996), S. 735-740 
    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 system of [Pt(CO)(AuPPh3)8]2+ represents an example of the spheroidal 18-electron cluster which consists of 283 atoms, 817 real-valence orbitals, and, eventually, 1634 complex spin-orbitals. The above system was investigated by an MO-LCAO-SCF study at the all-valence (nonempirical) quasi-relativistic and relativistic CNDO/1 levels. Owing to the complexity of the system under study, instead of an orbital interaction diagram, the density-of-state functions were generated. Their projections, obtained through net orbital populations, bear information about the positioning of MOS and eventual interaction of the AOS composing individual MOS. The platinum 5d orbitals exhibit a mixing with those of gold and contribute to only a few HOMOS; the rest of gold 5d orbitals, however, are situated at lower energies. © 1996 John Wiley & Sons, Inc.
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  • 162
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    International Journal of Quantum Chemistry 57 (1996), S. 63-71 
    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 new version of solutions in the form of an exponentially weighted power series is constructed for the two-dimensional circularly symmetric quartic oscillators, which reflects successfully the desired properties of the exact wave function. The regular series part is shown to be the solution of a transformed equation. The transformed equation is applicable to the one-dimensional problem as well. Moreover, the exact closed-form eigenfunctions of the harmonic oscillator can be reproduced as a special case of the present wave function. © 1996 John Wiley & Sons, Inc.
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  • 163
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    International Journal of Quantum Chemistry 57 (1996), S. 89-94 
    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 kinetic energy analysis of total energy differences in 115 atomic multiplet states is presented. We show by numerical restricted Hartree - Fock calculations that there is a reasonably accurate linear relationship between the kinetic energy of the electrons in open subshells and the total energy within a manifold of states arising from the same spn or s2pn (n = 2,3,4) electron configuration in main-group atoms. © 1996 John Wiley & Sons, Inc.
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  • 164
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    International Journal of Quantum Chemistry 57 (1996), S. 775-780 
    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 has already been shown that the use of the localized many-body perturbation theory (LMBPT) makes its possible to calculate the interaction energy at the correlated level in a straightfoward way. In this article, we show that the correlated part of the interaction energy, furthermore, can simply be decomposed into dispersion and charge-transfer contributions using the LMBPT scheme. The CH2O + NH3 model system was chosen for the above study. © 1996 John Wiley & Sons, Inc.
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  • 165
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    International Journal of Quantum Chemistry 59 (1996), S. 57-69 
    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 comparison of sixth-order Møller-Plesset perturbation energies (MP6) with the corresponding full configuration interaction (FCI) energies shows that in the case of equilibrium geometries MP6 values differ by just 1.7 mhartree. MP6 correlation energies turn out to be important for systems with oscillatory convergence behavior as well as for systems with considerable multireference character. Contributions from pentuple (P) and hextuple (H) excitations are mostly positive and smaller than 1 mhartree in the cases investigated. Initial oscillations in the convergence behavior of a MPn series result from positive fifth-order T energy contributions to the correlation energy. In these cases, MP6 correlation energies are relatively large (T contributions dominate the total correlation energy) and absolutely necessary when estimating the convergence limit of the MPn series. MP6 is an O(M9) method and, therefore, can only be used for relatively small electron systems. More economic alternatives are given by the approximated MP6 methods MP6(M8) and MP6(M7), which involve O(M8) and O(M7) operations, respectively. According to calculated absolute and relative energies, MP6(M7) is an attractive alternative to full MP6 because it offers reasonable sixth-order results for cost comparable to those of MP4. © 1996 John Wiley & Sons, Inc.
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  • 166
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    International Journal of Quantum Chemistry 59 (1996) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 167
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    International Journal of Quantum Chemistry 59 (1996), S. 1-2 
    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
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  • 168
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    International Journal of Quantum Chemistry 57 (1996), S. 465-470 
    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 results of semiempirical calculations on the heterofullerence C24N4 and its boron-nitrogen analogs B6N10C12 (the smallest CBN ball) are presented in accordance with considerations of chemical bondings and geometries. The structures and relative properties of the 28-atom cages, C28, C24N4, and B6N10C12, were investigated using semiempirical methods contained in the MOPAC program. C24N4 and B6N10C12 have Td and C3 symmetry, respectively. B6N10C12 has four geometric isomers, and their optimized structures were determined. The ionization energies, vibrational frequencies, IR intensities, and various thermodynamic properties (including entropy and heat capacity) for C24N4 and B6N10C12 were calculated by the MNDO method. The evidence suggests that a B6N10C12 cage is more stable than that of C24N4. Possible experimental methods to prepare B6N10C12 are also proposed. © 1996 John Wiley & Sons, Inc.
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  • 169
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 515-548 
    ISSN: 0271-2091
    Keywords: incompressible ; Navier-Stokes ; contravariant velocities ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: To analyse an incompressible Navier-Stokes flow problem in a boundary- fitted curvilinear co-ordinate system is definitely not a trivial task. In the primitive variable formulation, choices between working variables and their storage points have to be made judiciously. The present work engages contravariant velocity components and scalar pressure which stagger each other in the mesh to prevent even-odd pressure oscillations from emerging. Now that smoothness of the pressure field is attainable, the remaining task is to ensure a discrete divergence-free velocity field for an incompressible flow simulation. Aside from the flux discretizations, the indispensable metric tensors, Jacobian and Christoffel symbols in the transformed equations should be approximated with care. The guiding idea is to get the property of geometric identity pertaining to these grid-sensitive discretizations. In addition, how to maintain the revertible one-to-one equivalence at the discrete level between primitive and contravariant velocities is another theme in the present staggered formulation. A semi-implicit segregated solution algorithm felicitous for a large-scale flow simulation was utilized to solve the entire set of basic equations iteratively. Also of note is that the present segregated solution algorithm has the virtue of requiring no user-specified relaxation parameters for speeding up the satisfaction of incompressibility in an optimal sense. Three benchmark problems, including an analytic problem, were investigated to justify the capability of the present formulation in handling problems with complex geometry. The test cases considered and the results obtained herein make a useful contribution in solving problems subsuming cells with arbitrary shapes in a boundary-fitted grid system.
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  • 170
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 619-641 
    ISSN: 0271-2091
    Keywords: convective transport ; monotonicity ; finite volume ; boundary-fitted co-ordinates ; turbulence modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A formally third-order accurate finite volume upwind scheme which preserves monotonicity is constructed. It is based on a third-order polynomial interpolant in Leonard's normalized variable space. A flux limiter is derived using the fact that there exists a one-to-one map between normalized variable and TVD spaces. This scheme, which is relatively simple and quite compact, is implemented in a staggered general co-ordinates finite volume algorithm including the standard k-ε model and applied to the turbulence transport equations. A number of test problems demonstrate the utility of the proposed scheme. It is shown that in cases where turbulence convection is dominant, the application of a higher-order monotone convection scheme to the turbulence equations leads to results which are more accurate than those obtained using the first-order upwind scheme.
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  • 171
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 673-688 
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; projection methods ; operator splitting ; spectral element methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An approximate projection scheme based on the pressure correction method is proposed to solve the Navier-Stokes equations for incompressible flow. The algorithm is applied to the continuous equations; however, there are no problems concerning the choice of boundary conditions of the pressure step. The resulting velocity and pressure are consistent with the original system. For the spatial discretization a high-order spectral element method is chosen. The high-order accuracy allows the use of a diagonal mass matrix, resulting in a very efficient algorithm. The properties of the scheme are extensively tested by means of an analytical test example. The scheme is further validated by simulating the laminar flow over a backward-facing step.
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  • 172
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    International Journal for Numerical Methods in Fluids 22 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 173
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 755-770 
    ISSN: 0271-2091
    Keywords: Stokes ; multigrid ; Krylov subspace ; conjugate gradient ; conjugate residual ; Uzawa ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Discretization of the Stokes equations produces a symmetric indefinite system of linear equations. For stable discretizations a variety of numerical methods have been proposed that have rates of convergence independent of the mesh size used in the discretization. In this paper we compare the performance of four such methods, namely variants of the Uzawa, preconditioned conjugate gradient, preconditioned conjugate residual and multigrid methods, for solving several two-dimensional model problems. The results indicate that multigrid with smoothing based on incomplete factorization is more efficient than the other methods, but typically by no more than a factor of two. The conjugate residual method has the advantage of being independent of iteration parameters.
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  • 174
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 799-810 
    ISSN: 0271-2091
    Keywords: jets ; jet impingement ; turbulence ; k-ε model ; finite volume method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper reports numerical modelling of impinging jet flows using Rodi and Malin corrections to the k-ε turbulence model, carried out using the PHOENICS finite volume code. Axisymmetric calculations were performed on single round free jets and impinging jets and the effects of pressure ratio, height and nozzle exit velocity profile were investigated numerically. It was found that both the Rodi and Malin corrections tend to improve the prediction of the hydrodynamic field of free and impinging jets but still leave significant errors in the predicted wall jet growth. These numerical experiments suggest that conditions before impingement significantly affect radial wall jet development, primarily by changing the wall jet's initial thickness.
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  • 175
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 771-798 
    ISSN: 0271-2091
    Keywords: curved pipe flow ; variable cross-section ; secondary flow ; artery ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is concerned with steady, laminar flow of an incompressible Newtonian fluid in curved pipes of non-uniform cross-section. During the past decade a number of numerical solutions for flow in curved pipes have been obtained using progressively improved computational methods and technology; see e.g. Soh and Berger (Int. j. numer. methods fluids, 7, 733-755 (1987)) and Green et al. (Phil. Trans. R. Soc. Lond. A, 342, 543-572 (1993)) for relevant references. These results have been confined mainly to fully developed flow in pipes of constant cross-section. The present study deals with curved pipes of variable cross-section in which the velocity field is necessarily a function of the axial location along the pipe centreline in addition to the two cross-sectional co-ordinates. We use the finite difference method on a staggered grid with Newton's method to solve the Navier-Stokes equations. Results are calculated and presented for non-uniform pipe geometries with curvature ratios of 0ċ01 and 0ċ1. The velocity field for flow through curved pipes of non-uniform cross-section is compared with the corresponding results for flow through straight pipes of non-uniform radius and curved pipes of uniform radius, revealing important qualitative differences. The basic developments presented are applicable to a variety of flows in pipes, including those in arteries and piping systems.
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  • 176
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 835-849 
    ISSN: 0271-2091
    Keywords: non-linear first-order hyperbolic system ; collocation method ; upwinding ; thermal pipeline simulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Simulating thermal effects in pipeline flow involves solving a coupled non-linear system of first-order hyperbolic equations. The advection term has two large eigenvalues of opposite signs, corresponding to the propagation of high-speed sound waves, and one eigenvalue close to or even equal to zero, representing the much slower fluid flow velocity, which transports temperature. Standard collocation methods work well for isothermal flow in pipelines, but the stagnating eigenvalue causes difficulties when thermal effects are included. In a companion paper we formulate and analyse a new numerical method for the non-linear system which arises in thermal modelling. The new method applies to general coupled systems of non-linear first-order hyperbolic partial differential equations with one degenerate eigenvalue. In the present paper we focus on a linearized constant coefficient form of the thermal flow equations. This substantially simplifies presentation of the error analysis for the numerical scheme. We also include numerical results for the method applied to the fully non-linear system. Both the error analysis and the numerical experiments show that the difficulties that come from the application of standard collocation can be overcome by using upwinded piecewise constant functions for the degenerate component of the solution.
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  • 177
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 881-897 
    ISSN: 0271-2091
    Keywords: turbine cascade flows ; vortex shedding (periodic flows) ; compressible viscous flows ; turbulence and transition ; boundary layers ; multiblock meshes ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Periodic vortex shedding at the trailing edge of a turbine cascade has been investigated numerically for a subsonic and a transonic cascade flow. The numerical investigation was carried out by a finite volume multiblock code, solving the 2D compressible Reynolds-averaged Navier-Stokes equations on a set of non-overlapping grid blocks that are connected in a conservative way. Comparisons are made with experimental results previously obtained by Sieverding and Heinemann.
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  • 178
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 549-565 
    ISSN: 0271-2091
    Keywords: parallel computing ; multigrid method ; finite volume method ; block-structured grids ; incompressible flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper a parallel multigrid finite volume solver for the prediction of steady and unsteady flows in complex geometries is presented. For the handling of the complexity of the geometry and for the parallelization a unified approach connected with the concept of block-structured grids is employed. The parallel implementation is based on grid partitioning with automatic load balancing and follows the message-passing concept, ensuring a high degree of portability. A high numerical efficiency is obtained by a non-linear multigrid method with a pressure correction scheme as smoother.By a number of numerical experiments on various parallel computers the method is investigated with respect to its numerical and parallel efficiency. The results illustrate that the high performance of the underlying sequential multigrid algorithm can largely be retained in the parallel implementation and that the proposed method is well suited for solving complex flow problems on parallel computers with high efficiency.
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  • 179
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 581-601 
    ISSN: 0271-2091
    Keywords: unstructured grids ; incompressible viscous flow ; pressure-correction method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An unstructured grid, finite volume method is presented for the solution of two-dimensional viscous, incompressible flow. The method is based on the pressure-correction concept implemented on a semi-staggered grid. The computational procedure can handle cells of arbitrary shape, although solutions presented herein have been obtained only with meshes of triangular and quadrilateral cells. The discretization of the momentum equations is effected on dual cells surrounding the vertices of primary cells, while the pressure-correction equation applies to the primary-cell centroids and represents the conservation of mass across the primary cells. A special interpolation scheme s used to suppress pressure and velocity oscillations in cases where the semi-staggered arrangement does not ensure a sufficiently strong coupling between pressure and velocity to avoid such oscillations. Computational results presented for several viscous flows are shown to be in good agreement with analytical and experimental data reported in the open literature.
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  • 180
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 713-729 
    ISSN: 0271-2091
    Keywords: finite difference ; boundary conditions ; Navier-Stokes equations ; convergence analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite difference method for the Navier-Stokes equations in vorticity -streamfunction formulation is proposed to resolve the difficulty of the lack of a vorticity boundary condition at a no-slip boundary. It is particularly suitable for flows in regions with complicated geometries. Convergence with second-order accuracy in vorticity and velocity is established. In numerical experiments the convergence rates agree with theoretical predictions. Test results for the two-dimensional driven cavity problem and for the flow in expansion and contraction channels are given.
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  • 181
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 691-712 
    ISSN: 0271-2091
    Keywords: ELAFINT ; interface tracking ; solidification ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this work a mixed Eulerian-Lagrangian technique is devised, hereinafter abbreviated as ELAFINT (Eulerian-Lagrangian Algorithm For INterface Tracking). The method is capable of handling fluid flows in the presence of both irregularly shaped solid boundaries and moving/free phase boundaries. The position and shape of the boundary are tracked explicitly by the Lagrangian translation of marker particles. The field equations are solved on an underlying fixed grid as in Eulerian methods. The interface passes through the grid lay-out and details regarding the treatment of the cut cells so formed are provided. The issues involved in treating the internal boundaries are dealt with, with particular attention to conservation and consistency in the vicinity of the interface. The method is tested by comparing with solutions from well-tested body-fitted co-ordinate methods. Test cases pertaining to forced and natural convection in irregular geometries and moving phase boundaries with melt convection are presented. The capability developed here can be beneficial in solving difficult flow problems involving moving and geometrically complex boundaries.
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  • 182
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 149-150 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 183
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 867-879 
    ISSN: 0271-2091
    Keywords: optimal control ; optimization ; gas pipelines ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A general optimal control approach employing the principles of calculus of variations has been developed to determine the best operating strategies for keeping the outlet pressure of gas transmission pipelines around a predetermined value while achieving reasonable energy consumption. The method exploits analytical tools of optimal control theory. A set of partial differential equations characterizing the dynamics of gas flow through a pipeline is directly used. The necessary conditions to minimize the specific performance index come from the infinite-dimensional model. The optimization scheme has been tested on a pipeline subject to stepwise change in demand.
    Additional Material: 11 Ill.
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  • 184
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 915-917 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 185
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 186
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 919-919 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 187
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 211-221 
    ISSN: 0271-2091
    Keywords: backward-facing step ; particle-laden flow ; Lagrangian tracking ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Particle-laden flows are calculated for a classical laminar backward- facing step problem. The particle tracks are calculated using a recently developed exponential Lagrangian tracking scheme. The behaviour of the particle-laden flow is considered for various inlet for Reynolds number, Stokes numbers and void fractions. Doping the flow with low-Stokes-number particles has the effect of increasing the inlet inertia of the flow and this increases the strength of the recirculation behind the step. High-Stokes- number particles are dominated by gravitational effects which affect the flow accordingly. Differences between the single-phase flow and the particle-laden flows are therefore dependent on the Stokes number and increase linearly with void fraction.
    Additional Material: 9 Ill.
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  • 188
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 225-240 
    ISSN: 0271-2091
    Keywords: domain decomposition ; line Gauss-Seidel ; conjugate gradient ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The numerical discretization of the equations governing fluid flow results in coupled, quasi-linear and non-symmetric systems. Various approaches exist for resolving the non-linearity and couplings. During each non-linear iteration, nominally linear systems are solved for each of the flow variables. Line relaxation techniques are traditionally employed for solving these systems. However, they could be very expensive for realistic applications and present serious synchronization problems in a distributed memory parallel environment. In this paper the discrete linear systems are solved using the generalized conjugate gradient method of Concus and Golub. The performance of this algorithm is compared with the line Gauss-Seidel algorithm for laminar recirculatory flow in uni- and multiprocessor environments. The uniprocessor performances of these algorithms are also compared with that of a popular iterative solver for non-symmetric systems (the GMRES algorithm).
    Additional Material: 8 Ill.
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  • 189
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 283-296 
    ISSN: 0271-2091
    Keywords: laminar flow ; numerical modelling ; particle image velocimetry measurement ; rotating disc ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The fluid flow field within an enclosed cylindrical chamber with a rotating flat disc was calculated using a finite volume computational fluid dynamics (CFD) model and compared with particle image velocimetry (PIV) measurements. Two particular laminar cases near the Transitional flow regime were investigated: Reynolds number Re=2.5×1 4, chamber aspect ratio G (h/Rd)=0.2 and Re=4.2×104, G (h/Rd)=0.217. This enabled direct comparison with the numerical and experimental results reported by other researchers. The computational details and some major factors that affect the computed accuracy and convergence speed are also discussed in detail. PIV results containing some 4300 velocity vector points in each of seven planes for each case were obtained from the flow field parallel to the rotating disc. It was found that PIV results could be obtained in planes within the boundary layers as well as the core flow by careful use of a thin laser illumination sheet and correct choice of laser pulse separation. There was close agreement between numerical results, the present PIV measurements and other reported experimental and numerical results.
    Additional Material: 10 Ill.
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  • 190
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 191
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 297-311 
    ISSN: 0271-2091
    Keywords: large-eddy simulation ; numerical schemes ; mixing layer ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A posteriori tests of large-eddy simulations for the temporal mixing layer are performed using a variety of numerical methods in conjunction with the dynamic mixed subgrid model for the turbulent stress tensor. The results of the large-eddy simulations are compared with filtered direct numerical simulation (DNS) results. Five numerical methods are considered. The cell vertex scheme (A) is a weighted second-order central difference. The transverse weighting is shown to be necessary, since the standard second-order central difference (A′) gives rise to instabilities. By analogy, a new weighted fourth-order central difference (B) is constructed in order to overcome the instability in simulations with the standard fourth-order central method (B′). Furthermore, a spectral scheme (C) is tested. Simulations using these schemes have been performed for the case where the filter width equals the grid size (I) and the case where the filter width equals twice the grid size (II). The filtered DNS results are best approximated in case II for each of the numerical methods A, B and C. The deviations from the filtered DNS data are decomposed into modelling error effects and discretization error effects. In case I the absolute modelling error effects are smaller than in case II owing to the smaller filter width, whereas the discretization error effects are larger, since the flow field contains more small-scale contributions. In case I scheme A is preferred over scheme B, whereas in case II the situation is the reverse. In both cases the spectral scheme C provides the most accurate results but at the expense of a considerably increased computational cost. For the prediction of some quantities the discretization errors are observed to eliminate the modelling errors to some extent and give rise to reduced total errors.
    Additional Material: 3 Ill.
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  • 192
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 375-392 
    ISSN: 0271-2091
    Keywords: gates ; finite elements ; potential flow ; free surface ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Two-dimensional finite element analyses of two types of gate - (i) a conduit gate with pressure flow upstream of the gate and free surface flow downstream of the gate and (ii) a sluice gate with free surfaces both upstream and downstream of the gate - are done using ideal fluid theory. The conduit gate problem is solved using both Φ- and Ψ- formulations. Various methods of satisfying the boundary conditions were tested for both formulations. The ψ-formulation developed in the present study is found to converge faster for flows with Froude numbers less than 4, which are common in sluice gates. The results obtained from the present study are compared with results from analytical and experimental techniques available in the literature. The ψ-formulation developed in the present study is then used to solve the spillway gate problem, for which no analytical solution is available.
    Additional Material: 14 Ill.
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  • 193
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 411-428 
    ISSN: 0271-2091
    Keywords: composite grids ; adaptive grids ; multigrid parallelization ; Euler ; implicit scheme ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A method capable of solving very fast and robust complex non-linear systems of equations is presented. The block adaptive multigrid (BAM) method combines mesh adaptive techniques with multigrid and domain decomposition methods. The overall method is based on the FAS multigrid, but instead of using global grids, locally enriched subgrids are also employed in regions where excessive solution errors are encountered. The final mesh is a composite grid with uniform rectangular subgrids of various mesh densities. The regions where finer grid resolution is necessary are detected using an estimation of the solution error by comparing solutions between grid levels. Furthermore, an alternative domain decomposition strategy has been developed to take advantage of parallel computing machines. The proposed method has been applied to an implicit upwind Euler code (EuFlex) for the solution of complex transonic flows around aerofoils. The efficiency and robustness of the BAM method are demonstrated for two popular inviscid test cases. Up to 19-fold acceleration with respect to the single-grid solution has been achieved, but a further twofold speed-up is possible on four-processor parallel computers.
    Additional Material: 12 Ill.
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  • 194
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    International Journal for Numerical Methods in Fluids 22 (1996), S. 449-465 
    ISSN: 0271-2091
    Keywords: aeroacoustic ; vortex shedding ; solid rocket motor ; implicit or explicit method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present work is devoted to the numerical simulation of two important phenomena in the field of solid propellant rocket motors: the first is acoustic boundary layers that develop above the burning propellant; the other is a periodic vortex-shedding phenomenon which is the result of a strong coupling between the instability of mean flow shear layers and acoustic motions in the chamber. To predict the acoustic boundary layer, computations were performed for the lower half of a rectangular chamber with bottom-side injection. The outflow pressure is sinusoidally perturbed at a given frequency. For the highest CFL numbers the implicit scheme is not able to compute the unsteadiness in the acoustic boundary layer. With very low CFL numbers or with the explicit scheme the main features of the acoustic field are captured. To simulate the vortex-shedding mechanismin a segmented solid rocket motor, the explicit version is used. This computation shows a mechanism for ‘self-excited’ vortex shedding close to the second axial mode frequency. The use of the flux-splitting technique reduces substantially the amplitude of the oscillations. A few iterations are done with flux splitting, then the computation is performed without this technique. In this case both the frequency and the intensity are well predicted. A geometry more representative of the solid rocket motor is also computed. In this case the vortex-shedding process is more complex and pairing is observed.
    Additional Material: 12 Ill.
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  • 195
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 196
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    International Journal for Numerical Methods in Fluids 23 (1996), S. 307-308 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 197
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 569-580 
    ISSN: 0271-2091
    Keywords: magnetohydrodynamics ; Godunov ; upwind ; conservative ; plasma ; fusion ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper a higher-order Godunov method for one-dimensional solutions of the ideal MHD (magneto-hydrodynamics) equations is presented. The method uses a fluctuation approach and includes a new sonic fix and a new Roe averaging. After a short introduction the MHD equations in conservative form are given. The flux is rearranged such that the eigenstructure is not changed. This rearrangement allows full Roe averaging for any value of adiabatic index (contrary to Brio and Wu's conclusion). A new procedure to get Roe - averaged MHD fields at the interfaces between left and right states is then presented and some useful identities are given. Next the second-order-limited fluctuation approach is presented in full detail. The new sonic fix for MHD and the procedure for applying this fix to the sonic points are then given in detail. Numerical results obtained with the described method are presented. Finally, conclusions are given.
    Additional Material: 4 Ill.
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  • 198
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996) 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 199
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    International Journal for Numerical Methods in Fluids 23 (1996), S. 397-411 
    ISSN: 0271-2091
    Keywords: GMRES ; mild slope equation ; iterative solvers ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The mild slope equation in its linear and non-linear forms is used for the modelling of nearshore wave propagation. The finite difference method is used to descretize the governing elliptic equations and the resulting system of equations is solved using GMRES-based iterative method. The original GMRES solution technique of Saad and Schultz is not directly applicable to the present case owing to the complex coefficient matrix. The simpler GMRES algorithm of Walker and Zhou is used as the core solver, making the upper Hessenberg factorization unneccessary when solving the least squares problem. Several preconditioning-based acceleration strategies are tested and the results show that the GMRES-based iteration scheme performs very well and leads to monotonic convergence for all the test-cases considered.
    Additional Material: 10 Ill.
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  • 200
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    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 455-466 
    ISSN: 0271-2091
    Keywords: computational fluid dynamics ; unsteady incompressible flow ; method of lines ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A novel approach to the development of a code for the solution of the time-dependent two-dimensional Navier-Stokes equations is described. The code involves coupling between the method of lines (MOL) for the solution of partial differential equations and a parabolic algorithm which removes the necessity of iterative solution on pressure and solution of a Poisson-type equation for the pressure. The code is applied to a test problem involving the solution of transient laminar flow in a short pipe for an incompressible Newtonian fluid. Comparisons show that the MOL solutions are in good agreement with the previously reported values. The proposed method described in this paper demonstrates the ease with which the Navier-Stokes equations can be solved in an accurate manner using sophisticated numerical algorithms for the solution of ordinary differential equations (ODEs).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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