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  • 1990-1994  (269)
  • 1920-1924
  • 1990  (269)
  • Atomic, Molecular and Optical Physics  (269)
  • 1
    Electronic Resource
    Electronic Resource
    Modeling of real 20-component protein chains: Determination of the electronic density of states of aperiodic seven-component polypeptide chains containing strongly different amino acid residues (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 573-583 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To model a real 20-component protein chain, the results of the electronic density of states (DOS) of seven-component periodic and aperiodic polypeptide chains calculated on the basis of ab initio matrix block negative factor counting method are presented. The seven amino acid residues taken into account are rather different: glycine, serine, cysteine, asparagine, histidine, aspartic acid, and tryptophane. In the case of aperiodic chains, the energy states are found to be distributed over a much wider range of energy than in the corresponding periodic chains. In the intrinsic state, both periodic and aperiodic polypeptide chains are predicted to be insulators. The effect of the block copolymerization on the DOS distribution and the band gap values of both periodic and aperiodic polypeptide chains has been also investigated. Finally, the methods to calculate from the DOS curves hopping conductivities and the possibilities to compare them with experiment are outlined.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380407
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  • 2
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380501
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  • 3
    Electronic Resource
    Electronic Resource
    Methods for electron correlation on large molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 641-652 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-quality ab initio calculations, i.e., calculations including electron correlations with large atomic basis sets, have been restricted to relatively small systems due to their excessive demand on computer facilities. To extend these methods to large systems, one is faced with two problems: the steep (6 power) increase of the computational task with the molecular size, and the large number of electron repulsion integrals that must be stored and retrieved. We have recently introduced new computational methods where both these problems have been addressed. The local correlation method reduces the steep dependency of computational effort with molecular size without significant loss of accuracy by taking advantage of the localizability of the electronic structure. For electron correlation calculations integrals in the MO basis are needed in addition to the two electron integrals in the AO basis, and the only way electron correlation can be applicable to large systems is by a direct approach in the spirit of Almlof's direct SCF. We have recently extended the direct approach to post Hartree-Fock methods. Description of both these methods including their supercomputer implementations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380506
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  • 4
    Electronic Resource
    Electronic Resource
    Density functional calculation of transition metal cluster energy surfaces (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 691-698 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A quantum field mechanics of an electron subsystem in 3D physical space as the topology of compact atomic clusters with spontaneously broken local canonical symmetry is used for investigation of different types of microdefects in the condensed state of transition metals. The theory is illustrated with results of calculation of small compact Fen clusters (n = 2, 6, 14).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380510
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of molecular shape changes along reaction paths (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 713-726 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work, a detailed discussion and illustrative example are given for a new conceptual approach to the notion of similarity between nuclear configurations. We analyze the changes in molecular shape, as described by a topological characterization of molecular envelope surfaces, along reaction paths. This approach provides an independent definition of formal species along the path, defined in terms of molecular shape, rather than based on the curvature properties of the potential energy function. The two approaches are compared in this work, using the [1,3] hydrogen-shift in formic acid as an illustrative example. The reaction is studied at SCF and MP2 ab initio levels. Although the actual reaction paths are different, the molecular shape changes encountered along them are similar, indicating that the essential shape changes provide chemical information on a more fundamental level than do detailed reaction paths.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380512
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  • 6
    Electronic Resource
    Electronic Resource
    Applicability of multi-reference many-body perturbation theory to the determination of potential energy surfaces: A model study (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 761-778 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently written CI-based multi-reference many-body perturbation theory (MR-MBPT) program package is exploited to study a simple ab initio minimum basis set model involving four hydrogen atoms in a rectangular configuration. This model was examined earlier by several authors using both coupled cluster (CC) and finite-order MBPT approaches. Here we present the MR-MBPT results up to the 50th order and examine the effect of various shifting techniques on the convergence behavior of this approach. It is shown that in contrast with CC methods, both single and MR finite-order MBPT potential energy calculations are plagued with convergency and intruder state problems, which can be particularly severe when the latter approach is employed for non-degenerate situations.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380602
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  • 7
    Electronic Resource
    Electronic Resource
    Explicit algebraic form of coupled cluster equations for the PPP model of benzene with an approximate inclusion of triexcited clusters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 831-851 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An important role of model Hamiltonians for quantum mechanical description of the molecular electronic structure is discussed, and the effectiveness of the Pariser-Parr-Pople (PPP) model in calculations of molecular properties, in building of other models, and in various theoretical exploits is emphasized. The striking simplicity and transparence, yet remarkable reality and credibility, of this model is illustrated by applying the basic coupled cluster approach (CCD), as well as its extension approximating triexcited clusters (CCSDT-1), to the PPP model of benzene. The explicit final equations are obtained using the symbolic computation language MAPLE for both the orthogonal and nonorthogonal versions of the CC formalism. These equations are presented using the interface between MAPLE and the typesetting language TROFF. In this way, the explicit CC equations are obtained in terms of basic parameters of the model, starting from the CI description and showing their equivalence with those obtained via diagrammatic techniques. A new insight into the structure of CC equations at various levels of approximation is thus achieved and a useful model for electron correlation is provided.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380606
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  • 8
    Electronic Resource
    Electronic Resource
    The virial theorem scaling model for estimating the charge sensitivities of hydrogens in molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 853-863 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple variational model of hydrogens in molecules is presented, using the virial theorem (Fock) scaling of the wave function to account for the orbital relaxation due to a change in the number of electrons. The resulting interpolative formulas for the energy allow realistic predictions of the spin-nonpolarized or spin-polarized hardness (electron repulsion) parameters and other sensitivities of the hydrogen systems in molecules, including the realistic bare nuclei limit (N → 0) data.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380607
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  • 9
    Electronic Resource
    Electronic Resource
    Density matrices and density functionals. Proceedings of the A. John Coleman Symposium. Edited by R. Erdahl and V. H. Smith, Jr., D. Reidel, Dordrecht, 1987 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 869-869 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380610
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  • 10
    Electronic Resource
    Electronic Resource
    1990 sanibel symposia list of participants (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. XV 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381704
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  • 11
    Electronic Resource
    Electronic Resource
    Intramolecular hydrogen bonding in neutral glycine, β-alanine, γ-aminobutyric acid, and δ-aminopentane acid (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 45-53 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometries of those conformations of glycine, β-alanine, γ-aminobutyric acid, and δ-aminopentane acid, which are stabilized by an intramolecular hydrogen bond between the NH2-group and the COOH-group, have been optimized with ab initio SCF calculations. The 4-31G basis set was employed in this study. Geometry data and calculated vibration frequencies are given, and the effect of the ring size on H-bond formation is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381708
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  • 12
    Electronic Resource
    Electronic Resource
    30 years of sanibel symposia: Structure and activity of biomolecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 81-92 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To summarize the significance of the Sanibel Symposia in the field of “Structure and Activity of Biomolecules” is a Herculean task, meaning summarizing 30 years of the development of Quantum Biology in 30 minutes, which gives 1 minute per year. How does one do it? There are obviously many ways in which this cannot be done. One a priori conceivable way was to determine the most important (in the lecturer's eyes) contribution, discovery or paper for each of these consecutive 30 years and to present a list of potential laureates of what we could consider as an imaginary yearly Löwdin Prize. The author has tried the game but found it impraticable. A more reasonable solution seemed to be to trace the history of the main intellectual lines in the methods and themes which prevailed in the development of our knowledge on the Structure and Activity of Biomolecules during the period involved. It quickly turned out, however, that the scope was again so wide and its snapshot representation, the only feasible one, so dense and compact that it would have been reduced to the mere enumeration of the dozens of important, fundamental techniques and problems which have been dealt with during that time. So the author gave up this project too. Finally, after much hesitation, his choice went to a third procedure: the selection of the most important intellectual concept which had the most important impact on the development of the quantum-mechanical contribution to our understanding of structure-activity relationship in biomolecules. I believe this concept to be that of the electrostatic molecular potential, the introduction of which enabled the decisive step of moving over from the study of the structure and activity of small biomolecules or small constituents of the fundamental biomacromolecules to the study of these properties in the biomacromolecules themselves. Examples will be given which illustate this opinion.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381711
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  • 13
    Electronic Resource
    Electronic Resource
    Cyclododecapeptide analog of the polyhexapeptide of elastin: 2-D NMR and molecular dynamics studies (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 145-159 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hexapeptide, (APGVGV), is one of the repeating sequences found in the natural protein, elastin. The cyclododecapeptide, cyclo(L-Ala1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6)2, was synthesized and was found to undergo an inverse temperature transition leading to crystallization. Extensive NMR experiments have been carried out previously to evaluate its secondary structure in comparison to that of its linear counterpart, polyhexapeptide (APGVGV)n, directly and in terms of the concept of cyclic conformations with linear conformational correlates. Building on the previous work, this report adds 2-D NMR and molecular dynamics studies on the molecular structure of the cyclododecapeptide. From the 2-D COSY and 2-D NOESY experimental results, a reversal of the previous Gly3 and Gly5 resonance assignments in the cyclododecapeptide is reported. And in the 2-D NOESY study, a prominent NOE is found between the NH's of the two valine residues at position 4 and 6. Because the Val4 and Val6 residues are not adjacent to each other sequentially, the proximity of these two backbone hydrogens is used as an imposed constraint in constructing the molecular structure of the cyclododecapeptide. Molecular dynamics investigations were employed using the information from the 1-D and 2-D NMR experiments to arrive at potential molecular structures of the cyclododecapeptide. The characteristic secondary structural feature obtained is the expected Type II Pro2-Gly3 β-turn consisting of the 10-membered hydrogen bond between the residue-4 NH and the residue-1 C=O, a feature previously found in this and all other repeating peptides in elastin which contain the Pro2-Gly3 sequence.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381716
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  • 14
    Electronic Resource
    Electronic Resource
    Steric and electronic criteria for teratogenicity of short chain aliphatic acids (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 173-187 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Esters of short chain aliphatic acids are commonly used in industry as solvents which are easily metabolized to their acid analogs. Some of these aliphatic acids are also by-products of industrial products, e.g., 2-ethyl hexanoic acid is a metabolite of the plasticizer diethylhexyl phthalate and methoxy acetic acid is the principal metabolite of the glyco ether, 2-methyl ethanol. Many of these aliphatic acids exhibit a variety of toxic effects. Cytochrome P450 is involved in the metabolism of aliphatic acids resulting in liver toxicity by formation of a toxic metabolite. These acids also act as sedatives, possibly by occupying a hydrophobic site in the brain. Certain aliphatic acids have been shown to cause teratogenic effects in laboratory animals for which the mechanism is as yet unknown. The techniques of computational chemistry can be useful in helping to formulate such mechanisms and ultimately for computer-aided risk assessment of potentially toxic compounds. The current study focuses on developing reliable molecular indicators of the teratogenic behavior of selected aliphatic acids, by investigating the role of conformational, physical, and electronic properties. The geometries of the aliphatic acids used for analysis were optimized using CHARMm and AM1. Our results show that pKa and log P do not seem to be reliable modulators of teratogenic potency. By contrast, the conformation of the acid analogs, especially near the acid group, appears to be important for activity. These results implicate a possible mechanism of action involving a conformationally specific binding site or carrier protein.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381718
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  • 15
    Electronic Resource
    Electronic Resource
    A quantitative approach to structural similarity from molecular topology of reaction paths (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 1-13 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general discussion is provided on the changes in shape of a continuum of molecular surfaces along a reaction path. The path is partitioned in terms of the shape characteristics of the nuclear configurations. The most important feature of this partitioning is the eventual occurrence of a region where more than one shape can be associated with the molecular surface continuum. This region is a formal boundary range between different molecular shapes. Position and width of this range, as well as other related parameters, are introduced as measures of structural similarity along a reaction path. Examples of simple triatomic reactions are considered in order to show the relation between these similarity descriptors and the change of energy content along the path.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382405
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  • 16
    Electronic Resource
    Electronic Resource
    Theory of molecular orbital energy shifting induced by electrostatic external effects (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 89-96 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Self Consistent Reaction Field (SCRF) theory of electrostatic medium effects representation is used as the basis to derive the molecular orbital energy shifting induced by electrostatic external effects, coming from the interaction with a highly polarizable medium. A Perturbation-Variation methodology is used to perform the theoretical analysis. Under a first order perturbation approach, the shifting induced on the molecular electronic levels appears to be mainly dependent on the electronic polarization of the particular molecular orbital involved. As a result, it appears that the molecular orbital energy levels do not shift in a trivial constant amount by solvation, as it has been currently assumed. The result of our theoretical analysis shows that the solute electronic polarization term may be a relevant contribution to the molecular orbital energy changes induced by the environment. As an illustration of the usefulness of the present analysis, the alpha effect towards nucleophilic reactivity in solution of the OOH- and OH- ions is revisited.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382412
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  • 17
    Electronic Resource
    Electronic Resource
    N-representability of phase space functions for electrons (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 119-128 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conditions on one-electron Wigner and Husimi functions such that they correspond to n-representable charge density matrices are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382415
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  • 18
    Electronic Resource
    Electronic Resource
    Ab initio studies on hydrogen-bonded clusters: Structure and vibrational spectra of cyclic (HF)n complexes (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 129-140 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibrium structures of cyclic (HF)n clusters with n = 3, 4, and 6, and vibrational spectra of cyclic (HF)3 and (HF)4 were investigated with the aid of ab initio methods including electron correlation at a size-extensive level. Computed ground state properties such as equilibrium structures, stabilization energies, harmonic vibrational frequencies, and infrared intensities are compared with the corresponding quantities of HF monomer and dimer. Trends in the modifications of monomer properties as induced by cluster formation are monitored. Results for the structure and energetics of cyclic Dnh transition states of (HF)n with n = 2, 3, 4, and 6 are also reported.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382416
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  • 19
    Electronic Resource
    Electronic Resource
    A study of the Colle-Salvetti formula for the calculation of the correlation energy (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 213-223 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formalism of Colle and Salvetti for the calculation of the correlation energy of electronic systems has proven to be highly successful in a wide variety of applications. Several authors have applied the method and analyzed its usefulness.The Colle and Salvetti ansatz for the correlation energy isWe test the limits of validity for expression (2) by applying it to the series of ions isoelectronic with helium, (two-electron case) and beryllium, (four-electron case). We find that the approximation breaks down for sufficiently high Z. We also compare the results given by Eqs. (1) and (2). We find that although both expressions give the same result for the neutral He atom, in general they do not.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382422
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  • 20
    Electronic Resource
    Electronic Resource
    Correlations in extended systems: A microscopic multilocal method for describing both local and global properties (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 197-211 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We review the basic principles of the various coupled cluster (CC) methods based on an exponential form for the many-body wavefunction, and contrast them with the configuration-interaction (CI) method. Particular emphasis is placed on their applicability to problems in quantum chemistry. We prove that in all cases we can construct an energy functional which variationally determines both the ground-state wavefunction and the dynamic equations of motion for nonstationary states. As a result the equations of motion assume the familiar classical canonical Hamiltonian form in some well-defined (multibody) configuration space. We also thereby construct the expectation-value functional for an arbitrary operator in such a way that the Feynman-Hellmann theorem is preserved at all natural levels of truncation of the appropriate configuration space. We show in detail that only in the case of the recently introduced extended CC method (ECCM) is the expectation-value functional expressed fully in terms of linked (multilocal) amplitudes. The ECCM is thereby capable of describing such global phenomena as shape transitions and other stereochemical properties, and the large-scale behavior of the molecular energy surfaces. We illustrate our methodology on the one-body density matrix, which is now much more easily discussed than by conventional methods in quantum chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382421
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  • 21
    Electronic Resource
    Electronic Resource
    The evaluation of quantum chemical indices by the method of moments (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 251-262 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Moments present a convenient mean to describe molecular connectivity. The method of moments has been used to evaluate the total pi-electron energy Epi, the atomic charge Qr, and the free valence index Fr, in conjugated molecules. Because of practical reasons, only the moments up to some finite order L can be considered. Generally, the coefficients of the expansion of a property in terms of moments depend on L. In order to avoid this dependence, the expansion in terms of orthogonal polynomials has been used. Validity and convergence properties of such a method has been examined. The method has been also applied to some conjugated polymers.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382426
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  • 22
    Electronic Resource
    Electronic Resource
    Simple nonempirical calculations of the zero-field splitting in transition metal systems: I. The Ni(II)-Water complexes (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 295-309 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple nonempirical scheme is presented for calculating the splittings of ground state multiplets (the zero-field splitting) in transition metal complexes. The method employs single reference, single excitation CI calculations based on open-shell RHF. The spin-orbit coupling is described using an effective one-electron, one-center operators. The method is applied to the triplet state Ni(II) complexes with one to six water molecules. The validity of the second-order perturbation theory approach and of the spin-Hamiltonian formalism is found to be limited to slightly distorted octahedral systems. Generally, small changes in the geometries of the complexes are found to cause substantial variations of the splitting pattern.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382430
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  • 23
    Electronic Resource
    Electronic Resource
    Charge distribution and electric field gradients in YBa2Cu3O7 by band structure calculations (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 339-347 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From calculations using the full potential linearized augmented plane wave (LAPW) method, in which exchange and correlation effects are treated by the local density approximation (LDA), the electric field gradients (EFGs) of YBa2Cu3O7 are obtained on a first principles basis. The EFGs are computed at all atomic positions and a comparison with experimental values (magnitude and corresponding anisotropies) shows good agreement for Ba, Cu(1), and all oxygen positions while at Cu(2) the computed EFG agrees in symmetry but has only half the experimental value. However, the theoretical EFG would agree with the experimental value if only 0.07 electrons are transferred from dx2-y2 to dz2 symmetry.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560382434
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    Electronic Resource
    Electronic Resource
    On green's functions and their applications (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 393-404 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theory of Green's functions is briefly reviewed. It is discussed which properties of a quantum system and which physical processes can be described by Green's functions. A general approximation scheme to evaluate Green's functions and propagators is presented. Particular attention is paid to the one-particle Green's function and to the particle-particle propagator which is a relevant component of the two-particle Green's function. Several illustrative applications are presented and related to experiment.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382439
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    Electronic Resource
    Electronic Resource
    Classical dynamical analysis of the vibrational spectra for small polyatomic molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 429-446 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the study of three specific molecules, Na3(C2E″), HCN(X1Σ+), and O3(D1B2), each showing a distinctly different dynamical behavior at the energies studied, we show how techniques of nonlinear classical mechanics can be applied to simulate low resolution vibrational spectra and to extract the underlying dynamics from them. Particularly the importance of the single unstable periodic orbits in the chaotic regions of phase space is demonstrated.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382443
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  • 26
    Electronic Resource
    Electronic Resource
    Two different finite element schemes applied to quantum mechanical calculations (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 467-474 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The performance of the Zienkiewicz and of the reduced Hsieh-Clough-Tocher finite element schemes for the study of triatomic systems expressed in terms of hyperspherical coordinates is analysed here. Examples are given for the ion D2H+.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382446
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  • 27
    Electronic Resource
    Electronic Resource
    Two-photon transition moments as determined from the quadratic response function (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 487-499 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The matrix element for two-photon absorption is calculated as a residue of the general quadratic response function for a system subjected to an external time-dependent field. The matrix element is correct through first-order in electron correlation, and includes contributions in addition to those considered in previous calculations which were based on a truncated form of the Random Phase Approximation (RPA). Equations of motion are derived from the spectral representation of quadratic response, leading to equivalent expressions for two-photon absorption in the dipole length, mixed, and dipole velocity formulations. Because the transition moments evaluated in the three formalisms must be equivalent in a complete basis, the calculated results provide a measure of the adequacy of the basis set representation.As a test case, the X1σg+ (v = 0) → (E, F)1Σg+ (v = 6) two-photon process of H2 is considered. It is first demonstrated that agreement between length and velocity forms of the two-photon transition moment is obtained only through the consideration of all contributing terms. The vibrationally-averaged transition moment is decomposed into individual state contributions. It is found that the B1Σu+ and C1Πu-coupled matrix elements are comparable at the RPA level to values obtained at the near-full CI limit, and, although there is some disparity as to the relative weight of the remaining states, the total transition moment in the two formalisms are in good agreement. Using the transition moment obtained at the excitation frequency 1/2ωf, the integrated two-photon excitation cross-section is calculated. The value is in excellent agreement with the CI result and lies near the experimental error bars of the absorption cross-section determined from a single-beam measurement.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382449
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    Electronic Resource
    Dynamics of solitary waves induced by shock impulses in a linear atomic chainThis work was supported by ONR through NRL and the ONR physics division. (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 549-555 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The propagation of nonlinear waves induced by a shock impulse in a linear atomic chain of finite but large length is investigated numerically with a model interatomic potential. The shock impulse is initiated by giving the first atom in the chain an initial velocity vi toward its neighbor. We find that there exists a velocity vc such that for vi 〉 vc a soliton is produced by this impulse with a constant energy and supersonic velocity vs. Studies of the motion of the atom during the passage of this soliton reveal a behavior similar to that expected from the collision of hard spheres. However, for vi 〈 vc the induced pulse propagates below the speed of sound and gradually disperses through the emission of phonons. In the supersonic regime, vi 〉 vc, we find that there exists a velocity vm such that if vi 〉 vm, then vs 〈 vi, but if vi 〈 vm, then vs 〉 vi. Finally, in agreement with earlier studies using other model potentials, we find that if vi is large enough, a soliton can be generated with sufficient energy to spall an atom from the end of the chain.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382453
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    Electronic Resource
    Electronic Resource
    Molecular binding in free space and in cold dense plasmas (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 621-632 
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    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 theory of the potential energy curve of dimers Na2 and Be2 embedded in a cold dense plasma is first developed, starting from linear response theory plus a low-order gradient expansion. The results of this treatment are then reinterpreted, following the proposal of Perrot and March, in terms of bond midpoint properties. By comparison with full nonlocal density functional theory, the merits, and the limitations, of low-order gradient expansions are then assessed for Na2 and Be2 in dense plasmas. Use is made in this discussion of a pair potential extracted by inversion of the measured structure factor for liquid Na just above its freezing point. There is truly excellent agreement with the full density functional treatment of Perrot and March. The question is then addressed as to the relevance of the characterization by bond midpoint properties of the potential energy curve for dimers in a dense plasma to free space diatomic molecules and molecular ions. For H2+, it is demonstrated that such a characterization is exact. Heavier homonuclear diatoms are then considered, withi a low-order density gradient framework. It is emphasized that bond midpoint properties can again be used to characterize the potential energy curve. However, to obtain the electron density and its derivatives at the bond midpoint, it is now essential to solve the two-center problem in free space diatomics, whereas for Na2 and Be2 in sufficiently dense plasmas the superposition of one-center densities is an adequate starting point within the density functional framework.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382460
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    Electronic Resource
    Electronic Resource
    Overcoming the large-Z problem in quantum monte carlo (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 679-680 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Z6 scaling of computational effort in quantum Monte Carlo (QMC) results in part from a type of critical slowing down. This insight leads to an attack based on acceleration algorithms which modify the dynamics in Langevin-based simulations without changing the steady-state. Configuration space is more rapidly sampled and steps are inherently more decorrelated. A second approach uses a hybrid Metropolis-Green function Monte Carlo method which factors the core and valence wave function, and treats the former variationally with accurate trial functions, and the latter exactly in the presence of the variationally evoling core. This allows separation of the relevant core and valence time scales, and has sped up quantum simulations by over three orders of magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382465
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  • 31
    Electronic Resource
    Electronic Resource
    Valence bond theory: Progress and prospects (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 733-752 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382473
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    Electronic Resource
    A time-dependent molecular orbital approach to electron transfer in ion-atom collisionsWork partly supported by NSF Grants CHE-8615334 and CHE-8918925. (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 781-790 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A time-dependent molecular orbital approach has been developed for describing the dynamics of atomic and molecular interactions. Equations derived for the time-dependent electronic density matrices in the TDHF approximation are locally linearized in time with the use of a time-dependent reference density. It contains a time-dependent driving term due to the nuclear motions. Nuclear motions are obtained from the gradients of effective potentials which change with electronic states and account for couplings of nuclear and electronic motions. Results are presented for electron transfer in proton-hydrogen collisions, to compare to other calculations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382476
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    Electronic Resource
    Dynamical and spectroscopic studies of nonrigid molecules: Application to the thioacetone electronic ground state (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 835-841 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain a qualitative understanding of the torsional dynamics of the singlet ground state of thioacetone, ab initio calculations were performed with a 4-31G basis set + “d” orbitals on the sulfur atom. A two-dimensional potential energy function versus the rotational angles of the methyl groups was obtained. Using this potential, the Schrödinger equation for the double internal rotation was solved, for (CH3)2CS and (CD3)2CS, by expanding the torsional solutions on the basis of the symmetry eigenvectors of the G36 group. Frequency intervals of 148.72/122.24 cm-1 for the lowest A1 symmetry levels, was found, for (CH3)2CS/(CD3)2CS, in good agreement with the experimental values 153.2/114.7 cm-1. A discussion of the potential energy expansion terms suggests that the maxima of the potential are well described by the present calculations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382481
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    Electronic Resource
    Electronic Resource
    Mono- and dilayer analogues of crystalline atomic hydrogen (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 873-879 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As well as being of interest in their own right, many of the essential features of the lattice properties of crystalline atomic hydrogen should be interpretable in terms of the lattice properties of one- or two-layer hydrogen films. Here we present optimized equilibrium lattice parameters for monatomic hydrogen one- and two-layer films in several Bravais lattices as determined by all electron, full potential localdensity-approximation calculations.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382485
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    Electronic Resource
    Electronic Resource
    Studies on large electronic systems with PPP: Testimony of PPP's activity (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 485-495 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is nearly 40 years since the PPP method was proposed, and we demonstrate here that the method is still active in studying the electronic structures of very large conjugated systems and/or periodic systems. The kink (solition) problems in polyacetylene are solved with the UHF-PPP Hamiltonian, demonstrating that there appear several new features which have not been obtained without considering the interelectronic interactions of the PPP type. Next, the electron correlation effect in polyacetylene is discussed through the crystal orbital-PPP CI calculations. Finally, three-dimensional crystal orbital-CNDO calculations on graphite and black phosphorus are reported.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370417
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    Electronic Resource
    Electronic Resource
    Modification of DEWAR-PI to include ring strain (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 589-597 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous work has shown that the heats of formation of unstrained conjugated molecules can be reproduced with surpring accuracy by a semiempirical SCF MO treatment (DEWAR-PI) based on the Pariser-Parr-Pople (PPP) π SCF MO approximation. The original version failed to allow for ring strain. This deficiency has now been remedied in a new version (DEWAR-PI2).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370425
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    Electronic Resource
    Electronic Resource
    Nonlinear phase excitations in the PPP model of polyacetylene (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 559-588 
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    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 Pariser-Parr-Pople (PPP) method has revealed rich effects of the π electron Coulomb interaction in (CH)x. We discuss results obtained by the PPP model with the unrestricted Hartree-Fock (UHF) approximation and we show that concepts introduced by the PPP-UHF model give a new insight on Franck-Condon-type electronically excited states in (CH)x. In the first part of this paper, a brief review of the PPP-UHF model is given. We introduce phase and amplitude variables and show that solitons in the PPP-UHF model are phase excitations. In the second part of this paper, the effective Hamiltonian describing phase excitations is derived. We show that the phase Hamiltonian derived by the time-dependent Hartree-Fock approximation is the classical limit of the Hamiltonian derived by the bosonization method of Tomonaga, Luther, and others. The phase Hamiltonian has a family of new soliton solutions. These solitons are pure electronic excitations and correspond to the exciton and the magnon in (CH)x.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370424
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    Electronic Resource
    A tensor representation of the real spherical functions for the continuous group O3+ in cartesian coordinates: Example of eulerian rotations (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 655-662 
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    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 aim of this article is to give a practical way for the use of real spherical functions in another frame than the frame in which they have been defined. For instance, we calculate physical properties from a local frame and use them in the general frame, deduced one from the other by Eulerian rotations on the coordinates. The power of the method is in the use of cartesian coordinates and in the definition of a scalar product between these functions to set up the complete vectorial space generated by these representations of the group O3+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370504
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  • 39
    Electronic Resource
    Electronic Resource
    Quantum processes in semiconductors, 2nd ed. by B. K. Ridley (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 309-310 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370309
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  • 40
    Electronic Resource
    Electronic Resource
    Nonstandard turn of MDGI protein binding site of fatty acids? (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 311-319 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The growth-regulating factor MDGI belongs to the fatty acid binding proteins of which the amino acid sequence is known. Starting from hydrodynamic and dichroic measurements which yield estimations about mass, diameter, thickness, and content of α and β structure of the MDGI protein, we used theoretical methods to calculate the structures and electrostatic properties of selected β-chain sequences. The hydrophobic character of possible binding sites for fatty acids is demonstrated by the molecular electrostatic potential and field of this structures. A nonstandard turn element, formed by an H-bridge between polar side chains, Lys-Leu-Gly-Val-Glu, which connects two extended β chains, was found. Bound oleic acid could be able to stabilize such turn structure, which seems to appear also at the entrance of the cavity of two other proteins. The optimization of an oleic acid-turn van der Waals complex results in an interaction energy of about -50 kJ/mol originating mainly from the dispersion term and shows the participation of the four hydrophobic side chains Phe 64, Leu 66, Val 68, and Phe 70. Of these, at least Phe 64 and Phe 70 are known as possible binding sites of fatty acids.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380226
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  • 41
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    Electronic Resource
    MNDO CI study of the photoisomerization about polar double bonds (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 231-238 
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    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: Cis-trans photoisomerization of ethylene, some of its methyl and fluoro derivatives, methaniminium, and aminoborane was studied and twisted biradical geometries of these molecules in So, S1, and S2 states were optimized using the half-electron version of the MNDO method with configuration interaction. The results are quite satisfactory, in good agreement with available ab initio data.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380219
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  • 42
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    Electronic Resource
    Theoretical approach to reactions of polyatomic molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 191-208 
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    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 scheme for systematic reduction of the theoretical treatment of elementary reactions involving polyatomic molecules is described; it consists of (1) limitation to the energetically relevant regions of the nuclear configuration space (the reaction path and its near environs) and (2) restriction to the dynamically relevant subspace of the nuclear configuration space (the active modes). Starting from a generalized reaction path Hamiltonian of Nauts and Chapuisat allowing for the use of arbitrary curvilinear coordinates and several large-amplitude modes, the realization of the above-sketched scheme is discussed. A compilation of recent work along these lines, mostly based on the simplified Miller-Handy-Adams reaction path Hamiltonian, is given with particular emphasis on applications of a statistical adiabatic model.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380214
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  • 43
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    Theoretical study of single-electron capture in the N5+ + He and O6+ + He collisions by means of ab initio methods (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 615-621 
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    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: Partial cross sections of single-electron capture on the n = 3 levels have been determined theoretically for the N5+ + He and O6+ + He collisions by means of a semiclassical method using ab initio potential energy curves and radial and rotational coupling matrix elements. The different behavior of these two isoelectronic systems is fairly well reproduced by our calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380504
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  • 44
    Electronic Resource
    Electronic Resource
    Localized orbitals for the description of molecular interaction (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 665-673 
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    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 intermolecular interaction between the molecules CH2O and NH3 was investigated by the supermolecule method. The interaction energies were first calculated at the ab initio SCF level, and the electron correlation was included via second-order Møller-Plesset perturbation theory (MP2). The basis set superposition error (BSSE) was taken into account by the counter-poise (CP) method. The occupied and the virtual canonical molecular orbitals (CMOS) of the supermolecule were separately localized by the Boys' procedure. The correlation correction was calculated by the many-body perturbation theory (MBPT) in the localized representation. Contributions of the third- and fourth-order localized diagrams were added to those of the second-order canonical diagram. This procedure gives a correction nearly equivalent to that of MP2. The possibility to separate LMO contributions responsible for the dispersion interaction was investigated.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380508
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    Announcement (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 759-759 
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    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
    URL: http://dx.doi.org/10.1002/qua.560380515
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  • 46
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    On the long way from the Coulombic Hamiltonian to the intermolecular energy surfaces: Concluding remarks at the tromsø conference, June 20-22, 1989 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 741-758 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After a brief review of the main results given at the conference, the general properties of the Coulombic Hamiltonian for a system of electrons moving in a framework of moving atomic nuclei - considered as point charges - are discussed. Since this Hamiltonian is invariant under translations and rotations, the total momentum and the total angular momentum are constants of motion, which means that it is possible to separate the motion of the center of mass and the rotation of the system as a whole. Even if these separations are simple in principle, they lead to a mixing of the electronic and nuclear coordinates that complicates the transformed Hamiltonian. The general features of this Hamiltonian are discussed both in pure quantum mechanics and general quantum theory dealing with wave functions Ψ respective density matrices ρ or system operators T. The principles of the latter are derived from five simple axioms, and it is shown that pure quantum mechanics is a special case of the general theory and that the analogy between these two approaches is essential for the “economy of thinking.” It is indicated that the general theory of the shape and topology of the energy surface 〈H〉 = TrHΓ and its critical points, as a function of the system operator Γ involving both electronic and nuclear coordinates, is a very difficult mathematical problem and that calculation of this surface even for simple molecular systems represents a formidable computational problem, which has to be solved in order to be able to understand the nature of chemical reactions from first principles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380514
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    The effect of interlayer interactions on chemisorption pattern stability: Hydrogen atoms on graphiteDisclaimer: This work represents the views of the authors and not necessarily the official position of the U.S. Military Academy, the U.S. Army, or any other governmental agency. Work of the U.S. Government, not subject to copyright restrictions. (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 799-817 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extended Hückel band calculations, frontier crystal orbital analysis, and degenerate-level perturbation theory are used to evaluate the effect inclusion of bulk-layer interactions has on the relative stabilities of ordered overlayers. Five patterns of hydrogen atoms chemisorbed on unreconstructed graphite (11% coverage) are examined for the Bernal (ABABAB…) and registered (AAA…) three-dimensional stackings. The single-layer two-dimensional approximation for graphite is found not to be entirely satisfactory for the type of chemisorption pattern stability questions addressed in this paper.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380604
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    Electronic Resource
    Hyperspherical harmonics. Applications in Quantum Theory. By. J. Avery, Kluwer Academic Publishers, Dordrecht, Boston, London, 1989 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 867-867 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380609
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  • 49
    Electronic Resource
    Electronic Resource
    Tunnel effect in proton transfer (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 521-531 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Semiempirical computations were carried out to determine the tunneling rates in the case of coupled motion of two protons along the reaction coordinate. The following molecular systems were studied for medium intermolecular distances (A - B = 2.72 or 2.75 Å); +AH - BH - A, where A was NH3 or H2O and BH was HF or H2O. In the cases where the bridge was HF, solvation was modeled with just one water molecule attached to each side of the perpendicular axis through HF at 2.75 Å. Coupled motion of three protons was also included in the case of H3O - H2O - H2O - H2O.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380403
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  • 50
    Electronic Resource
    Electronic Resource
    Application of molecular orbital graph theory to vibrational problems of finite chain systems (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 559-572 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A generating function approach based on molecular orbital graph theory is presented that provides a straightforward way of obtaining the secular polynomials and energy bands for repeated unit systems from polynomial recurrence expressions. The possibility of obtaining the analytical energy-level spectrum of the system can also be predicted. These results are then used to discuss the vibrational problems of finite chain systems with single- and double-component lattices. It seems to be the first report describing the vibrational states of an (AB)N chain.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380406
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    Electronic Resource
    Announcement call for contributions to paper symosium on algebraic methods in quantum chemistry and solid-state theory (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 608-608 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380411
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    Electronic Resource
    EUCHEM conference tromsø, June 20, 1989 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 613-613 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380503
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    Electronic Resource
    Numerical determination of the electronic structure of atoms, diatomic and polyatomic molecules. Edited by M. Defranceschi and J. Delhalle, Kluwer Academic Publishers, Dordrecht, Boston, London, 1989 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 865-865 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380608
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  • 54
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    Electronic Resource
    Editorial (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. V 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381702
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  • 55
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    Electronic Resource
    Ab initioMO calculations of the chlorophyll dimer in the photosynthetic reaction center (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 93-101 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular orbital (MO) calculations of the chlorophyll dimer have been carried out, using the structure determined by Deisenhofer et al. for Rhodopseudomonas viridis. AMOSS, a new MO program package developed by the NEC quantum chemistry group for vector computers was used. The dimerization energy is estimated to be 16.1 kcal/mol, indicating that the dimerization of the chlorophylls at the present geometry seems to be unfavorable. Two possible reasons are discussed. One is the underestimation of π-π interactions between the chlorophylls. The other is the influences by the proteins surrounding the dimer.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381712
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    Electronic Resource
    Brownian simulation of protein association and reaction (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 55-71 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Brownian dynamics simulation method has been developed as an alternative to conventional molecular dynamics or simple analytical diffusion theories in order to study the diffusive dynamics and interaction between two whole proteins. Highly detailed and realistic models of protein structures and their electrostatic interactions were used based on an atomic-level spatial description. The Coulombic and excluded volume torques and forces between the molecules are computed at each Brownian time step and rotational and translational diffusional trajectories are generated between interacting proteins. For the first time the rotation of both proteins is included. This method has been applied to study the association and electron transfer between horse heart ferrocytochrome c and yeast cytochrome c peroxidase, horse heart ferricytochrome c and bovine ferrocytochrome b5 and the electron self-exchange of P. aeruginosa cytochrome c551. Accurate residue charge assignments at the appropriate pH and ionic strength are computed by the Tanford-Kirkwood theory with surface accessibility modification. Accurate interaction potentials are computed by iterating solutions of the Poisson-Boltzmann equation on a grid. The low dielectric constant inside proteins, electrolyte screening effects, and irregular protein surface topography are taken into account. Realistic criteria for determining the successful docking of the cytochromes are based on a combination of mutual orientation of heme planes and heme edge-to-edge distance. We examine the role of electrostatic charge distribution and solvent mediation in the facilitation of protein-protein docking prior to the electron transfer step. We expect that, with improvements, the Brownian dynamics method will be capable of predicting the effects of site-directed mutagenesis on protein-protein and protein-ligand interactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381709
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    Introduction (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. XIII 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381703
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  • 58
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    Electronic Resource
    Adenine-Thymine proton relay: Electric field and environmental effects on point mutation DNA (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 35-44 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation of ionic base pair adenine-thymine (A+-T-) has been studied using the ISCRF-AM1 (Inhomogeneous Self-Consistent Reaction Field-Austin Model 1) approach. In the vacuum, the potential energy shape for the proton relay is the same as the one previously obtained by ab initio methods, namely, a single-well energy profile characterized by a monotonically increasing energy function. When the effects of an electric field and a polarizable medium are included via ISCRF formalism, a double-well potential energy profile is obtained. The consequence of these results for spontaneous mutagenesis has been quantitatively discussed, using a parabolic and Eckart type potential for tunneling rate calculations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381707
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    Electronic Resource
    Change of the frontier electronic orbitals due to substitutional impurities in large chemical or biological molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 73-80 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecule whose electronic structures are poorly understood, in some cases, can be thought of as another perhaps well-understood “host chemical molecule” with substitutional “impurities.” From this point of view, the Green's function technique in solid state physics can be extended to investigate the change due to substitutional impurities in large chemical or biological molecules of the frontier electronic orbitals - the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO). These orbitals are the ones most active in chemical reactions, and are conceptually very similar to the valence band and conduction band states of semiconductors. Substitutional impurities will often introduce new “deep” electronic states into the gap between the HOMO and LUMO states of the original molecule and these states will have the following properties. (i) The likelihood that an impurity will produce a state in the gap depends on the site of the impurity. (ii) For impurities on a particular site, the wavefunction of the gap state will be relatively independent of the impurity. (iii) Only a small fraction of the deep level wavefunction (typically 10%) will lie within the impurity's cell and the largest part (about 40-50%) will be on the impurity's nearest-neighbor atoms. (iv) The derivative of the energy of the impurity state with respect to the central-cell impurity potential dE/dV is approximately equal to the probability of the gap-state electron being found on the impurity's site.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381710
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    Simulation of a sodium dodecylsulfate micelle in aqueous solution (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 103-117 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics calculations have been used to probe the structure of a small sodium dodecylsulfate micelle in aqueous solution. The simulation system consisted of 42 dodecylsulfate ions, 42 sodium ions, and 1901 deuterated water molecules in a periodically replicated box. Electrostatic interactions were treated with an Ewald method. Over the course of a 182 ps trajectory, the micelle remained compact and roughly spherical with the hydrocarbon chains on the inside and the sulfate groups on the outer perimeter. The micelle displayed only small fluctuations in shape and had an average radius of about 15 Å. Relatively little water penetrated beyond the head-group region and the inner core (9 Å in radius) was devoid of water. On average each chain was found to have about three gauche defects. The average chain conformation in the micelle interior has been contrasted with that of an isolated monomer in solution. The counter ion distribution has been examined and compared with results from a previous simulation of a sodium octanoate micelle.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381713
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    Electronic Resource
    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382401
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  • 62
    Electronic Resource
    Electronic Resource
    Introduction (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. XIII 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382403
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    Electronic Resource
    International Journal of Quantum Chemistry -  A Journal Devoted to Quantum Theory and Computations in Chemistry, Condensed Matter Physics, and Biology; Editorial-Program and Policies (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. XI 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382402
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  • 64
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    Electronic Resource
    Calculation of equilibrium geometries and harmonic frequencies by the LCGTO-MCP-local spin density method (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 29-39 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results are presented from linear combination of Gaussian type orbitals-model core potential-local spin density calculations on equilibrium geometries and harmonic frequencies of several small main group and organometallic molecules. The equilibrium geometries were obtained by minimizing the norm of an approximate analytical energy gradient while the frequencies were obtained by numerical differentiation of these gradients. Comparison with experimental data indicates that the approximate gradients yield accurate results which typically agree better with experiment than those of the Hartree-Fock method and compare favorably with commonly used correlated techniques.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382407
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    Density functional calculations with simulated annealing - isomers of S7X [X = O, S, Se], Se8, O8 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 141-151 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Density functional calculations - with a local density approximation for the exchange and correlation energy - provide a numerically efficient method for determining total energy variations in molecules. Coupled with molecular dynamics techniques such as simulated annealing, they provide a scheme for probing large regions of configuration space in molecules. We outline the main features of the method and apply it to different ring isomers of S7O, S8, S7Se, Se8, and O8.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382417
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  • 66
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    Electronic Resource
    Electronic structure of the V2+ impurity states in ZnSe (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 187-195 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report on the results of first-principles, SCF calculations of the electronic structure of the unrelaxed, substitutional, divalent Vanadium impurity in ZnSe. The effects of the surrounding ZnSe crystalline environment and of electron correlation on the SCF results reported here have been studied and are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382420
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    Electronic Resource
    Electronic Resource
    Ab initio models for Be81 and Be87 metal clusters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 225-240 
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    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 self-consistent field calculations are reported for electronic states of beryllium clusters comprised of 81 and 87 atoms. The clusters correspond to the tenth and eleventh coordination shells of a central Be with internuclear separations derived from the lattice constants of the bulk metal. Ab initio effective core potentials have been employed to replace the 1s electrons, therey reducing the complexity of the calculations. In addition, the use of the full D3h point group symmetry of the clusters results in a substantial reduction of the number of two-electron integrals that must be computed and processed. Binding energies, orbital energies, electric field gradient, nuclear-electrostatic potential, diamagnetic shielding constant, second moments, and Mulliken populations are calculated for selected electronic states. Systematic trends toward bulk behavior with increasing cluster size, as found in earlier cluster studies, continue to appear for the electric field gradient and quadrupole moment of Be81. Anomalous behavior, however, is observed in Be87. This is attributed to distortional effects due to the addition of atoms in planes above and below the Be81 cluster along the principal axis of symmetry.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382423
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    Electronic Resource
    Strategies for walking on potential energy surfaces using local quadratic approximations (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 263-276 
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    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 algorithm for locating stationary points corresponding to local minima and transition states on potential energy surfaces is further analyzed. This method utilizes local gradient and Hessian (i.e., first and second energy derivative) information to generate a series of “steps” that are followed to the desired stationary point. By designing the step sequence to move energetically downhill in all coordinates, local minima can be found. By stepping uphill along one local eigenmode of the Hessian while minimizing the energy along all other modes, one locates transition states. Key elements of this development are more efficient parameterization of the step vector in terms of quantities that permit the direction (i.e., uphill or downhill), and length of the step to be carefully controlled, and implementation of the ability to explore “side channels” as attractive options occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382427
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  • 69
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    Electronic Resource
    Siegert resonance calculations - real and divergence-free (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 321-326 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The calculation of virtual states or resonances is formulated as the solution of a system of coupled real differential equations with suitable boundary conditions and solved by means of a finite difference method. The results are compared to similar results calculated with other techniques. In most of the cases we found very good agreement.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382432
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    Electronic Resource
    Möbius-Type quadrature of electron repulsion integrals with B functions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 349-363 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The numerical properties of a three-dimensional integral representation [J. Grotendorst and E. O. Steinborn, Phys. Rev. A 38, 3857 (1988)] of the electron repulsion integral with a special class of exponential-type orbitals (ETO's), the B functions [E. Filter and E. O. Steinborn, Phys. Rev. A 18, 1 (1978)], are examined. B functions span the space of ETO's. The commonly occurring ETO's can be expressed in terms of simple finite sums of B functions. Hence molecular integrals for other ETO', like the more common Slater-type orbitals, may be found as finite linear combinations of integrals with B functions. The main advantage of B functions is the simplicity of their Fourier transform which makes the derivation of relatively simple general formulas for molecular integrals with the Fourier transform method possible. The integrand of the integral representation mentioned above shows sharp peaks causing, in the case of highly asymmetric charge distributions, slow convergence of the quadrature method used by Grotendorst and Steinborn. Quadrature schemes are presented which utilize quadrature rules based upon Möbius transformations. These rules are well suited for the numerical quadrature of functions which possess a sharp peak at or near a single boundary of integration [H. H. H. Homeier and E. O. Steinborn, J. Comput. Phys., 87, 61 (1990)]. Numerical results are presented which illustrate the fact that the new quadrature schemes are also applicable in case of highly asymmetric charge distributions.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382435
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    Comparison of theoretical methods for the determination of the Li+ Affinities of neutral and anionic first- and second-row bases (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 365-373 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of the Li+ complexes with the bases NH3, H2O, HF, PH3, H2S, HCl, and HCN and with the corresponding deprotonated anions have been optimized using second-order Møller-Plesset perturbation theory with the 6-31+G(d,p) basis set. Single-point calculations on all species were performed using the 6-31+G(2d,2p) basis set using the following correlation methods: many-body (Møller-Plesset) perturbation theory at second (MP2), third (MP3), and fourth (MP4) order; the linearized coupled-cluster method (LCCM); the averaged coupled pair functional (ACPF); configuration interaction with all single and double excitations (CISD); and CISD with the Davidson and Pople corrections. The computed lithium ion affinities of the neutral bases vary between 15 and 40 kcal/mol, while the values for the anionic bases are between 145 and 190 kcal/mol. The effect of correlation on the lithium ion affinities varies between about -5 and +2 kcal/mol. For each neutral base, the lithium ion affinities computed with the various correlated methods agree with each other to between 0.1 and 1 kcal/mol. For the anions, the various correlated methods agree with each other to between 0.5 and 3 kcal/mol. Agreement with the available experimental data is within the estimated uncertainties in the latter. Structural differences between corresponding first- and second-row complexes reflect differences in the strength of the electrostatic interaction due to differences in the charge distribution.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560382436
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    A theoretical approach to the design of reduced band gap noncorrosive electrodes for photoelectrochemical solar cells (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 419-427 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preliminary results from our charge self-consistent LCAO band structure (CSCBS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a (1:1) mixture of β-PbO2 and TiO2 (both rutile). The band gaps for the constituents (β-PbO2 and TiO2) and the 1:1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTiO3 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382442
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  • 73
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    One-Center matrix elements for the morse oscillator (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 481-485 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have derived exact analytical expressions for the diagonal matrix elements 〈n|xk|n〉, k = 1, 2, for the Morse oscillator using the operator algebra of the two-dimensional harmonic oscillator and the method of the parameter differentiation. These expressions avoid the roundoff error present in other relations. The method can be extended to other integrals where k 〉 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382448
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    Reliable isotropic and anisotropic dipolar dispersion energies, evaluated using constrained dipole oscillator strength techniques, with application to interactions involving H2, N2, and the rare gases This reasearch was supported by a grant from the Natural Sciences and Engineering Research Council of Canada. (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 501-520 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dipole oscillator strength distributions (DOSDS), which are reliable in the sense of yielding accurate results for the various dipole properties of molecules, can be constructed if sufficient input information is available. The DOSDS are constructed from extensive experimental and theoretical information, including oscillator strength and photoabsorption cross section data, and are constrained to reproduce accurate refractivity measurements of the relevant dilute gases and to satisfy oscillator strength sum rules. The techniques for obtaining the DOSDS, and related properties, are well established for the evaluation of reliable isotropic dipolar dispersion energies. In this paper they are extended to the evaluation of anisotropic dipole properties, with particular emphasis on anisotropic dispersion energies. The approach used will be illustrated with applications involving H2, N2, and the rare gases. Also included will be brief discussions on (i) the use of reliable results for the dipole-dipole and triple-dipole dispersion energies in constructing complete two- and many-body potential energies and (ii) the advantages of constrained DOSD methods, relative to other approaches, for determining all the dipole properties of molecules.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560382450
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    Anion-Antisite defects in GaAs: As and Sb (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 563-567 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present results of selfconsistent, first-principles calculations of total energies for AsGa and SbGa in GaAs. We confirm that both impurities in the substitutional Td site behave as double donors, and the first internal excitation appears at around 1 eV. For the neutral systems we obtain a metastable minimum in the total energy surface in a configuration with the impurity atom displaced toward the interstitial site; the transformation to this metastable configuration, however, is not expected to be operative for the SbGa defect.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382455
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    Quantum-Mechanical interpretation of the local many-body potential of density-functional theory (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 569-584 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The local many-body potential of density-functional theory is thus far understood in its mathematical context as the functional derivative of the exchange-correlation energy functional of the density. In recent work we have attempted to provide a physical interpretation for this potential. We interpret it as the work required to move an electron against the electric field of its Fermi-Coulomb hole charge distribution. Implicit in this interpretation is that the potential is path-independent. For symmetric systems this is rigorously the case. For systems where this may not be the case, the potential may be derived from an effective charge distribution given by the divergence of the field, thus ensuring its path independence. Also implicit as a consequence of the total Coulomb hole charge being zero is that the asymptotic structure of the potential is entirely due to the Fermi hole charge distribution, and thus known precisely. The potential lies explicitly within the rubric of density-functional theory in that within the exchange-only approximation it satisfies the exchange energy virial theorem sum rule and all scaling properties that the exact exchange potential must satisfy. The potential does not satisfy the virial theorem sum rule for the correlation energy, and consequently a term proportional to the difference between the interacting and noninteracting system kinetic energies must be added for the sum rule to be satisfied exactly. The formalism differs from density-functional theory in that it is not derived from the variational principle for the energy, thus obviating the requirement of determining functional derivatives, as well as allowing for the study of excited states. The interpretation also leads to insights into the exact Slater exchange potential, and other approximation schemes such as the Xα method, and local density and gradient expansion approximations. The results of application to few-electron atomic and many-electron metallic surface inhomogeneous electronic systems are remarkably accurate when compared with other theoretical calculations and experiment.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560382456
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    Coupling of electrons and lattice wave packets in superconducting metastable states formed at high pressure (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 717-719 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382471
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    Evidence of strong electron-phonon coupling in the high Tc copper oxide superconductors (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 693-699 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fundamental mechanism responsible for high temperature superconductivity in the copper oxides is still not known. In view of this, it is important to consider how best to account for the normal state properties of these materials in the hope of characterizing the excitations which are relevant to the superconducting instability. Results of local density functional approximation (LDA) calculations are presented of the electronic density response, which yields predictions of phonon frequencies and electron-phonon interaction strength as well as structural parameters and structural instabilities. Structural properties and phonon frequencies are in excellent agreement with experiment in both La2-xMxCuO4 and YBa2Cu3O7. Theoretical evidence is also presented for strong nonlocal contributions to the electron-phonon coupling in these materials.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382468
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    A scaled force field for polyenes derived from ab initio calculations including electron correlation effects (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 721-732 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometries and harmonic force constants were calculated for trans- and gauche-butadiene and for trans- hexatriene using SCF and electron correlation (ACPF) methods. By comparing the results of these two procedures trends in the errors of the SCF values are discussed. Although diagonal SCF force constants are usually too large in relation to correlated results, the opposite is true (in absolute value) for several off-diagonal force constants referring to the carbon backbone. Scaling techniques are used in order to correct for these deficiencies and also for anharmonicity effects. On that basis scaled SCF force fields and vibrational frequencies were calculated for trans-polyenes up to 14 carbon atoms and for the infinite chain.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382472
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    PPP (Peel) calculations on iron porphyrins and iron phthalocyanine. Charge distribution and charge transfer (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 547-558 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Semiempirical molecular orbital calculations within a modified PPP method, the Peel method, have been performed in order to study the electronic structure and properties of porphyrins and phthalocyanines. It is found that the calculations can reproduce the results from more sophisticated ab initio calculations. It is found that the electronic reactions may take place at the metal atom and in the axial direction. The role of the porphine plane seems to be that of an electron buffer, keeping the electronic population in the porphyrin plane constant. A mechanism is suggested where electron transfer reactions can take place by change in the molecular geometry, as for example by vibrations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370423
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370501
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  • 82
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    Dependence of valency on geometry for configuration interaction wave functions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 685-699 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Earlier definitions of valencies of atoms, molecules, and molecular orbitals are extended to configuration interaction (CI) wave functions. Using these definitions, valencies both at equilibrium and nonequilibrium geometries of molecules are calculated at the CI level and compared with non-CI results. CI valency correlation diagrams are obtained. Valency variation with bond length using correlated wave functions is found to behave properly unlike in the case of SCF wave functions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370507
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    Potential surfaces and nonadiabatic couplings in ionic systems: A study of the (O2H)+ interactions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 729-746 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The adiabatic potential energy surfaces (PES) which are most likely to be involved in the elementary mechanism presiding over charge-exchange and direct inelastic collisions between O2 molecules and collimated beams of protons are discussed. The general behavior of Diatomics-in-molecule (DIM) model interactions is analyzed in great detail as a function of the molecular vibrational coordinate and of the other internal nuclear coordinates. The general features of the lower two PES are discussed, and the corresponding nonadiabatic coupling terms between these surfaces are also computed and analyzed. These model results turn out to provide very useful indications on the specific dynamical features that are to be considered responsible for the inelastic, vibronic transitions observed in the target molecule during collisional experiments.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370603
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  • 84
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    A CI pseudopotential-based description of the low-lying states of Ag O2 (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 785-796 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extensive SCF-LCAO-MO variational and perturbative configuration interaction (CI) calculations framed within an effective core potential approximation have been performed to determine the two experimentally observed geometrical isomers of Ag O2 and the interconversion route between them. These structural forms, associated to the ground-state local minima, yield virtually the same energy, and their spontaneous interconversion is strongly indicated, which agrees fairly well with the experimental measurements. The reaction Ag + O2 → Ag O2 was theoretically analyzed along a CI fully optimized energy pathway for the ground and various excited states, within C2v and Cs symmetry. Although a tight-ion pair (Ag+ O2-) character is predicted for the ground state at the equilibrium geometries, its dissociation leads to neutral rather than to ionic fragments. The study of the reaction path within Cs symmetry shows an avoided crossing between the ground state and another 2A″ potential curve where the former correlates adiabatically with the reactants Ag(2S) + O2(1Δg). This indicates that the formation of the complex proceeds via a reactive state of molecular oxygen. The higher 2A″ electronic curves correlate with the metal 2P excited state, and the oxygen binding is found to be less favorable. The present results are shown to have an important bearing on the experimentally known catalytic properties of oxygen adsorbed on silver surfaces.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370607
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    Triplet-singlet splitting of the alkali metal clusters: Example of the Li6 clusters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 149-161 
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    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 influence of the geometry on the specifics of the electronic structure of Li6 clusters is studied in detail, since planar and three-dimensional lithium hexamers are found to be of comparable stability. The ab initio CI investigation of the Li6 isomers yields almost degenerate lowest singlet and triplet states for certain cluster geometries. Simple criteria for the energy gap between the lowest triplet and singlet state are derived, and their applicability is demonstrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380210
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370101
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  • 87
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    Two-center molecular repulsion integrals over slater functions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 51-68 
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    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: For the general two-electron two-center integral over Slater functions, use of the Neumann expansion for the electron-electron interaction term yields the standard auxiliary functions. These are expanded and integrated explicitly by two independent methods. The resulting simple analytic formula for the total integral is completely general, requiring only the Slater function quantum numbers and exponents and the internuclear separation. Hence all two-electron hydrid, coulomb, exchange, and one-center integrals are considered. The efficiency of calculation of this expression is compared with those of other methods, indicating an order of magnitude improvement in speed over recursion for the exchange integral.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370105
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    The many-body expansion of the potential energy function for elemental clusters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 95-102 
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    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 many-body expansion of the potential energy function of elemental clusters is examined in general terms in regard to its convergence for microclusters and the bulk phase. The systems Ben and Lin are examined in detail. For Li it is clear that the many-body expansion has no low-order convergence, but it is shown that a potential of the form \documentclass{article}\pagestyle{empty}\begin{document}$$ V = aV^{(2)} + bV^{(3)} $$\end{document} gives good binding energies for Lin (3〈n≤9) and also a good value for the heat of atomization of the bcc crystal.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370108
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  • 89
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    A representation of the McClelland method of graph splitting. Stack graphs (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 113-120 
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    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: McClelland's rules on graph splitting can be represented using the generalized graph notation. Generalized graphs are edge- and vertex-weighted graphs, which are becoming important to chemical problems. By this the McClelland method of graph splitting has a wider range of applications. “Stack graphs” are constructed from identical “base graphs” by connecting corresponding vertices from one base to another. Their eigenvalues are related to the eigenvalues of the base graph. Two- and even three-layered graphs may be used as a simple model for the inter-ring interaction in a cyclophane.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370202
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  • 90
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    Coherence in disordered condensed matter. III: H+ and OH- ionic conductance and proton transfer reactions in aqueous solutions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 155-165 
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    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 physical context of the high ionic conductivity of the H+ and OH- ions in aqueous solutions is considered. Quantum dynamical aspects of the mobility of these ions are investigated, especially within the framework of the complex scaling method (CSM). It is argued that the high ionic mobilities under consideration are due to quantum delocalization of the ions as well as mass interference of the H+ ions with water protons. This effect is formally described with the aid of the coherent-dissipative structures, which become spontaneously created in the solution owing to the thermal motion. In particular, (1) a novel connection between the proton transfer rate (as measured by NMR) and the mobilities of the considered ions (as determined by conductivity measurements) is derived. Additionally, (2) a relation connecting the activation energies of the above reaction rates with the ionic mobilities is found. The above relations contain no fitting parameters. Comparisons with experimental results is made, which also reveals the predictive power of the present CSM treatment in the field of microdynamical processes in condensed phases.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560370206
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    Announcement (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 207-207 
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    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
    URL: http://dx.doi.org/10.1002/qua.560370210
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  • 92
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    Quasiparticle band structure and exciton spectrum of hexagonal boron nitride using second-order Møller-Plesset many-body perturbation theory (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 241-248 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Many-body perturbation theory up to second-order in the Møller-Plesset partitioning has been used to calculate the quasiparticle band structure of hexagonal boron nitride, treated as a periodic two-dimensional system. It was found that correlation leads to an essential narrowing of the fundamental gap. The exciton spectrum has been calculated using the first order irreducible vertex part with Hartree-Fock and quasiparticle band structure data. It was found that the exciton binding energy amounts to about 10% of the fundamental gap (for the first singlet excitation).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370304
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  • 93
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370601
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  • 94
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370401
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  • 95
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    Robert G. Parr (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 313-313 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370403
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    The origin of PPP theory (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 349-371 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An historical account is given of the part played by the author in the development of PPP theory in the early 1950s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370408
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  • 97
    Electronic Resource
    Electronic Resource
    On the connection between semiempirical molecular orbital theories and effective hamiltonians: A constrained variational point of view (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 415-422 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The idea of interpreting the semiempirical MO theories from a constrained variational point of view is explored. A density-based approach is developed for calibrating the parameters of useful semiempirical Hamiltonians of molecular electronic structure theory. Results of some numerical experiments with model Hamiltonians of constrained variational origin are reported.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370412
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  • 98
    Electronic Resource
    Electronic Resource
    From PPP-MO theory to all-valence electron calculations of ionic and excited states in organic molecules (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 465-483 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: PPP MO theory initiated in 1953 a reliable SCF approach to excited states in multielectronic systems. Further developments, such as Del Bene-Jaffé's CNDO/S method, modified Pople's CNDO all-valence electron (AVE) approach to improve the results but maintained some basic troubles of this theory which were not in the PPP method. A new approach to SCF-MO-NDO calculations with a priori chosen parameters and configuration interaction of singly excited states is developed in this paper from the ground considerations of the PPP method and it is called CNDOL. Thus, AVE NDO approximations have been modified in order to take into account independent monocentric terms in the Fock matrix elements for each kind of azimuthal quantum number atomic orbitals in the basis set. The only input data are Slater exponents, valence state ionization potentials, and electron affinities of each kind of atomic orbital. No parameters are empirically adjusted to fit results to experimental or previous accurate theoretical data. CNDOL is suitable for obtaining theoretically consistent results in polyatomic systems which are too large to be treated by more sophisticated procedures. Applications to hydrocarbons are shown which compare PPP results with the new AVE approach derived from it here.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370416
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  • 99
    Electronic Resource
    Electronic Resource
    Peel, a modified PPP method, applied on the spectra of some nucleic acid bases (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 517-528 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison between some different modifications of PPP methods is made. It is noticed that each modification may have its advantages but that some may be more suitable for interpretation of electronic spectra than others. It is also pointed out that PPP methods may allow more accurate descriptions of π properties than all-valence methods, such as CNDO/S.The Peel method, a PPP method especially adapted to reproduce the lowest π → π* transitions of a few reference molecules, has been applied to studies of the pyrimidine bases cytosine, uracil, and thymine. The obtained frequencies and oscillator strengths compare favorably with experimental evidence. The calculated polarization directions are in general agrreement with measurements. In case of cytosine a reinterpretation of measurements is suggested.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370420
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  • 100
    Electronic Resource
    Electronic Resource
    Localization in aromatic and conjugated hydrocarbons. Shape studies on canonical PPP one-electron eigenfunctions (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 529-537 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The localization properties of the π-electron system of some aromatic and conjugated hydrocarbon molecules have been investigated. The π orbitals have been obtained using a standard PPP-SCF procedure. The shape analysis was carried out using the novel concept of the relation between the localization measure and structural entropy. According to our investigations the π-electron system of these aromatic molecules is more localized than expected. The eigenstates seem to show one-dimensional characteristics with a decay rate generally faster than exponential. Linear chains, on the other hand, have rather delocalized orbitals. As a byproduct we have found that in certain systems some states exhibit step-function-like behavior, similar to bond-centered charge density waves.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370421
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