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  • 1995-1999
  • 1985-1989  (411)
  • 1986  (411)
  • Computational Chemistry and Molecular Modeling  (411)
  • Nuclear reactions
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  • 1995-1999
  • 1985-1989  (411)
Year
Keywords
  • 101
    Electronic Resource
    Electronic Resource
    Chemisorption of O and O2 on Ag(110): An LCGTO-LSD cluster study (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 829-842 
    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 part of a study aimed at better understanding of molecular and dissociative chemisorption of oxygen on Ag(110), linear combinations of Gaussian type orbitals-local spin density (LCGTO-LSD) calculations have been performed for O, O-, O2, O-2, O2-2 and a variety of silver clusters interacting with O or O2.For atomic O adsorption a very small cluster, Ag4, chosen to model the long-bridge site already affords very good agreement with both recent EXAFS experiments and recent ab initio calculations. We calculate O to be 0.25 Å above the surface (exp. 0.2 Å). The Ag4—O vibrational frequency is estimated to be 400 cm-1, in reasonable accord with the experimental EELS value of 325 cm-1.Determination of the geometry for O2 (ads.) and, ultimately, of the dissociation path are far more difficult tasks. An extensive search for local minima in the vicinity of the LB site is being carried out. Results to date for small, Ag2 and Ag4, clusters have furnished insight into the factors influencing the structure. Overlap between the π* orbital of the O2 moiety and Ag s functions is a key factor; that is, there is an important covalent component of the binding. For geometries with O2 parallel to the surface, this is achieved by twisting the O2 fragment with respect to the [11¯0] grooves (geometries either parallel or perpendicular to the grooves yield zero π‖*-s overlap by symmetry). The structure with O2 perpendicular to the surface also achieves reasonable overlap and lies close in energy to the most stable ‘parallel’ geometry.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290421
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  • 102
    Electronic Resource
    Electronic Resource
    Basis-Set dependence of exterior electron distributions of molecular orbitals (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 677-688 
    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: Interior electron densities are divided from exterior electron densities (EED), when an effective boundary is introduced. The EED concept was used to study the quality of wavefunction tails; the basis-set dependence of ab initio MO for NH3 was studied from EED. The EED for the nonbonding orbital (3a1) increases dramatically with the size of basis sets, whereas that for the bonding orbital (1e) shows saturation even at the double zeta class. Although inclusion of polarization functions always gives the better total energy the EED (3a1) may either increase or decrease or decrease depending on the choice of the smaller or the larger exponents. The conventional choice of the polarization functions for 6-311G* and 6-311G* was found to yield worse wavefunction tails than the case of 6-311G. Much better results were obtained with the more diffuse polarization functions. The (11s7p)/[5s4p] set designed for Rydberg states as well as the 6-311 + G set proposed for negative ions gave excellent results comparable to the case of the near Hartree-Fock calculation with 56 CGTO. Considerable improvements were also achieved for 4-31G and 6-311G sets, when the exponent for the outermost s-type function was modified. The largest EED (3a1) gave the best agreement with the experimental ratio of EED's derived from Penning ionization electron spectroscopy.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290410
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  • 103
    Electronic Resource
    Electronic Resource
    Structural deformations of the DNA double helix in the first stages of DNA transcription studied with a simple model (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 717-735 
    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 very simple model of DNA in biological media, consisting of electric charges related to the phosphate groups and to counterions immersed in structured media of constant permittivity, is introduced and tested with the study of a model for the first stages of the DNA transcription.This process is modeled into two steps involving three ‘states’: (1) the DNA system at the equilibrium, (2) the DNA with a small portion deprived of counterions, and (3) the DNA with a partial opening of the double helix in correspondence of the zone deprived of counterions.An extensive investigation involving as variable parameters the length of the DNA specimen (from 31 to 1511 base pairs), the amount of condensed counterion charge (from complete compensation to zero), and the geometrical parameters identifying the local opening has shown that the proposed transcription mechanism is reasonable, and that the DNA model considered here may fill a gap between accurate models including all the interactions - and employed at present for small fragments - and unstructured models addressed to inspect the behavior at the limit of infinite DNA length.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290413
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  • 104
    Electronic Resource
    Electronic Resource
    Interpretation of the vibrational spectra of matrix-isolated uracil from scaled ab initio quantum mechanical force fields (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 799-815 
    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 vibrational spectrum of uracil trapped in an argon matrix has been interpreted based on ab initio Hartree-Fock SCF calculations with a split-valence 4-21 basis set. The directly computed theoretical general valence force field was scaled with empirical scale factors in order to correct for the systematic errors originating in the limitation of the theoretical model. Scale factors transferred from related molecules provided a priori prediction of fundamental frequencies and intensities, permitting several corrections to be proposed for earlier assignments. Using the observed spectrum with the few altered assignments, a new set of scale factors was optimized to give the best force field available from combined consideration of the experimental and the theoretical data. For unknown reasons, the out-of-plane force field predicted a spectrum agreeing slightly less well with experiment than did the in-plane force field. However, the overall agreement between theory and experiment provided additional support for the assumptions involved in the method. The computed force fields were compared with others available from previous work. The comparison demonstrated the importance of expanding the energy surface around the true energy minimum and of using a proper scaling procedure. Previous scaled CNDO/2 calculations were found to be surprisingly good despite the large corrections required and the fact that they were made at an incorrect geometry.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290419
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  • 105
    Electronic Resource
    Electronic Resource
    On the minimization of the global variance in the 1-Reduced local-energy matrix (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 867-873 
    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: By minimizing the global variance in the 1-reduced local-energy matrix E1(X1; X1′), subject to the normalization of the 1-reduced density matrix ρ1(X1;X1′), one derives an integral matrix equation for E1(X1;X1′) as a functional of ρ1(X1;X1′) at the location (X1;X1′) of an arbitrary member of an N (≥ 2)-particle system. The implications for the possible local improvement in the accuracy of approximate wave functions through the imposition of global constraints are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290424
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  • 106
    Electronic Resource
    Electronic Resource
    Adiabatic coordinate separation and large N-dimensional limit in two-electron ions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 897-908 
    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 1/N expansion is used to generate semiclassical effective potentials for two-electron ions. These potentials can be considered an improvement over the conventional ones computed by Lin and Fano for the full two-electron coulomb potential insofar as they incorporate some of the quantum mechanical effects. No falling into the nucleus is allowed. Furthermore, the minima of these effective potentials are in surprising agreement with those computed by Fano, Macek, and Lin. This would indicate that the collective variable R, associated with N = 6, leads to a much smaller expansion parameter N, making the adiabatic separation more justified. The role and significance of these broken symmetry solutions with geometric localization are discussed as well as generalizations. The procedure is semiclassical in the sense that the kinetic energy becomes negligible by having a large effective mass.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290427
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  • 107
    Electronic Resource
    Electronic Resource
    Generalized 1/Z expansion for heteronuclear molecules (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 949-958 
    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 first studied empirical regularities in various series of heteronuclear diatomic molecules between the energy E, the total number of electrons N, the equilibrium distance Re and Z̄ = (Z1Z2)1/2 where Z1e and Z2e are the nuclear charges in the diatom. In particular, for various alkali halide series, Re2|E|/N5/3 is shown to correlate rather simply with Z̄Re3. Some theoretical basis is afforded by generalizing the 1/Z expansion used early by the writers in work on homonuclear diatomics. Finally, when Z2/Z1 → ∞, a model is presented which predicts a finite asymptotic bond length and this prediction is confronted with available experimental data for both heteronuclear diatoms and for the polyatomic series CH4 to SnH4.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290431
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  • 108
    Electronic Resource
    Electronic Resource
    Electronic structure and chemical bonding of the dimer of bis(η5-cyclopentadienyl)ytterbium methyl (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1017-1024 
    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 electronic structure, charge distribution, and chemical bonding of the dimer of bis-(η5-cyclopentadienyl)ytterbium methyl have been studied by an unrestricted INDO program made applicable for the lanthanoid compounds [1]. The bond order, composition, and the nature of the bridge bonds have been discussed. The existence of weak interaction between two ytterbium atoms was shown.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290436
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  • 109
    Electronic Resource
    Electronic Resource
    The effect of correlation energy (MP2) on computed vibrational frequencies (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1127-1137 
    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 IR frequencies of cyclopropene and methylenecyclopropene were computed with inclusion of correlation (MP2/6-31G*). These along with those of ethylene obtained earlier by Pople were compared with SCF results (DZ + P). It was found that the MP2 frequencies agreed better with experiment, but that the order of the bands remained the same as those computed without correlation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290511
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  • 110
    Electronic Resource
    Electronic Resource
    Continuum states of the hydrogen molecule with the R-Matrix method (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1033-1042 
    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 interaction of low-energy electrons with H+2 and ligh with H2 is analyzed using the R-matrix method including both coupled state and polarization effects ab initio. Particular attention is paid to the energy region containing low-lying H*2 resonances which converge to H+2 A 2Σ+u. Resonances in both elastic scattering and the photoionization asymmetry parameter, β, are presented. At low photon eneries, satisfactory results for vibrationally resolved photoionization are obtained using the adiabatic nuclei approximation. The use of nonadiabatic techniques for higher energies is discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290502
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  • 111
    Electronic Resource
    Electronic Resource
    Hartree-Fock cluster study of interstitial transition metals in silicon (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1059-1066 
    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 of a Hartree-Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in silicon. A Si10 cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core electrons is represented by an effective potential. Characteristic for the electronic structure of the low-lying states of the neutral, singly positive, and doubly positive ions in silicon is the presence of fairly delocalized but still predominantly transition-metal (3d)-like orbitals of t2 and e symmetry. For all ions the energy of the weighted average of the terms belonging to a configuration is lowest for the configuration with maximum occupation of the t2 orbitals. Ground states with maximum spin multiplicity are found for all ions, except Ti0.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290505
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  • 112
    Electronic Resource
    Electronic Resource
    Electronic structure of highly doped conducting polymers (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1165-1176 
    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: Three-dimensional energy-band calculations on highly doped donor and acceptor compounds of polyacetylenes have been carried out using experimentally suggested channel and intercalation models for the structure of these conducting polymers. The band structures can be very well approximated by the superposition of bands calculated for the polymer chains without the presence of dopants and the bands calculated for the guest chains or layers, strongly supporting the rigid-band model (RBM) for these structures. The absence of strong mixing between the guest and host orbitals explains the small perpendicular to the chain band widths (and corresponding resonance integrals as well) supporting interchain hopping models for the charge transport in these systems. The results are compared with calculations on graphite intercalation compounds (C8K and C7Br).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290515
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  • 113
    Electronic Resource
    Electronic Resource
    An ab initio molecular orbital study on the stacking interaction between nucleic acid bases: Dependence on the sequence and relation to the conformation (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1253-1261 
    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 stacking interaction energies between nucleic acid bases in A DNA and B DNA are calculated by means of the ab initio molecular orbital method. The calculated values agree well with the experimental values of stacking enthalpy changes. The stacking interaction energy is shown to be highly sequence dependent, particularly when the sequence includes guanine or cytosine. The possibility is shown that the conformation of a DNA double helix fragment is determined by the constituent stacking interaction. Electrostatic energy is the cause of the sequence dependency of the stacking energy, while charge transfer and dispersion energies contribute to the overall stability.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290522
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  • 114
    Electronic Resource
    Electronic Resource
    Structure and properties of nonclassical polymers. III. Magnetic characteristics at finite temperaturesSecond communication: Theoretica chimica acta 67, 211 (1985). (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1325-1337 
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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: Within the Ising model, the two-dimensional alternant nonclassical polymers display magnetic order at finite temperatures and are characterized by a nonzero critical point Tc.It is shown that magnetic ordering at finite temperatures occurs when interchain interactions in a quasi- dimensional nonclassical altemant polymer are taken into account.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290528
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  • 115
    Electronic Resource
    Electronic Resource
    Quantum theory of dielectric relaxation in polar solids (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1365-1372 
    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 novel approach to the impurity dipole relaxation in polar solids is described in which the dipole reorientational sites are formed by an appropriate electron - phonon coupling interaction. The electronic states used for a two-site formulation are defined as ones pertaining to the impurity and/or the associated intrinsic point defect. The theory takes into account the adiabaticity of the electron transfer in addition to the barrier-controlled ionic tunneling. It compares favorably with available experimental relaxation-time data on alkali halides.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290531
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  • 116
    Electronic Resource
    Electronic Resource
    Final state effects in the photoionization process (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1437-1455 
    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: Different methods to take into account many body effects in photoionization processes are discussed. Numerical results are shown for some indirect methods, several approximations within the Green's function formalism, and for potential models. The suitability of the Green's function method for the investigation of satellite structure is considered.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290536
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  • 117
    Electronic Resource
    Electronic Resource
    Thermal and state-selected rate constant calculations for O(3p) + H2 → OH + H and isotopic analogs (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1463-1482 
    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 a new parametrization (based on ab initio calculations) of the bending potentials for the two lowest potential energy surfaces of the reaction O(3P) + H2, and we use it for rate constant calculations by variational transition-state theory with multidimensional semiclassical tunneling corrections. We present results for the temperature range 250-2400 K for both the rate constants and the intermolecular kinetic isotope effects for the reactions of O(3P) with D2 and HD. In general, the calculated rate constants for the thermal reactions are in excellent agreement with available experiments. We also calculate the enhancement effect for exciting H2 to the first excited vibrational state. The calculations also provide information on which aspects of the potential energy surfaces are important for determining the predicted rate constants.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290538
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  • 118
    Electronic Resource
    Electronic Resource
    The case of disordered two-dimensional electron systems (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1525-1533 
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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 investigate the question of the existence or nonexistence of mobility edges that separate the localized and extended states in two-dimensional disordered electron systems treated within the Anderson model. Evidence is produced to show that the mobility edges exist if the amount of disorder is less than a critical value. The following three different agruments are presented: (1) exact enumeration of self-avoiding walks that contribute to the renormalized perturbation series of self-energy whose convergence (divergence) indicates localization (delocalization); (2) “quantum percolation” in a strongly disordered binary alloy; and (3) influence of magnetic field on localized and extended states (the quantum Hall Effect problem).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290543
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  • 119
    Electronic Resource
    Electronic Resource
    Calculated electronic spectra of model ferric cytochrome P450 complexes (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1575-1589 
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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: Restricted open-shell ground state properties and electronic spectra of two closely related low-spin, ferric, 6-coordinate, model cytochrome P450 complexes, one with a methyl mercaptide and the other a mercaptan as the second axial ligands, have been calculated with a newly modified, semiempirical INDO-SCF-CI method. The sensitivity of the calculated spectra to protonation of the sixth axial ligand, and the ability of the method to predict characteristic spectral features for the complexes investigated, are determined. Assignment of transitions, including xy- and z-polarized transitions, are made and compared with experimental observations where available. In particular, the origin of the anomalous split Soret spectrum observed in low-spin ferric complexes with mercaptide but not a mercaptan is investigated. Finally, a two part hypothesis is presented which provides a general explanation for the origin of both the observed split Soret and the red-shifted normal Soret in various ferrous and ferric P450 complexes in terms of the ground state orbital characters and simple symmetry considerations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290547
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  • 120
    Electronic Resource
    Electronic Resource
    Molecular theory and cooperative mechanism of shock waves-induced detonations in energetic molecular crystals (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1625-1634 
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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: At a microscopic level, two molecular models, respectively one- and two-dimensional, for describing the shock-induced detonationmechanism of an energetic crystal have been previously successively presented (after initiation).We put together, here, their characteristic features, and we discuss their respective contributions inorder to define the molecular and crystalline conditions that a crystal fulfills to sustain a shock induced wave detonation. The two-dimensional model which allows longitunal but also transversal atomic motions, has enabled us to elicit the crystalline structure in relation with the existence of a wave detonation propagation in the crystal or not. By comparison to detonation experiments the coherence of the models is performed. It may thus be possible to form an idea as to why a molecular compound can detonate through a shock wave.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290550
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  • 121
    Electronic Resource
    Electronic Resource
    Announcement (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1685-1685 
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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: No. Abstract.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290553
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  • 122
    Electronic Resource
    Electronic Resource
    Double symmetrization and the linearly independent spin eigenfunctions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1687-1695 
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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: It is shown that the exclusion principle merely requires the electrons to be divided into two distinct groups, then, according to our assumption of the distinguishability of electrons, its mathematical representation can be the spatial double antisymmetrization or the spatial-spin antisymmetrization; in the latter case an auxiliary spin double symmetrization is also required in order to distinguish the two types of electrons. The second requirement is used to recognize the fact that, although all electrons can be assumed to be indistinguishable under certain condition, their natural characteristic of two distinct groups must still be preserved.It is further shown that the double antisymmetrization (or double symmetrization) determines the spin quantum number M, whereas the Löwdin spin projector for nonorthogonal eigenfunctions and the Wigner matric basis for orthogonal eigenfunctions will decide the spin quantum number S, Both the spatial double antisymmetrizer and the spin double symmetrizer will reject all the unnecessary eigenfunctions and project out only one unique set of linearly independent eigenfunctions.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290602
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  • 123
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    Construction of orbital angular momentum eigenfunctions for many-particle systems by harmonic projection (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1735-1743 
    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: Formulas are derived which allow the direct construction of total orbital angular momentum eigenfunctions for many-particle systems without the use of Clebsch-Gordan coefficients. One of the equations is closely analogous to Dirac' identity for the total spin operator. This equation describes the action of L2 on a function of the particle coordinates in terms of a class operator of the symmetric group and a "contraction operator." A general projection operator for constructing symmetric eigenfunctions of L2 is presented.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290606
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    Calculation of SN 1 + N 2 ⊃ SN1 ⊗ sn 2 and U(n1 + n2) ⊃ u (n1) ⊗ u (n2) subduction coefficients by using spin graph (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1779-1787 
    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: By use of the graphical method of spin algebra, simple, and closed expressions for SN1+N2 ⊃ SN1 ⊗ SN2 and U(n1 + n2) ⊃ U(n1) ⊗ U(n2), subduction coefficients are derived.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290610
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    A quantum mechanical investigation into the fine specificity of the antibodies to soman, BE2, and CC1 (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1845-1845 
    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.560290618
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  • 126
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    Announcement (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1847-1847 
    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.560290619
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  • 127
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    Announcement (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1849-1849 
    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.560290620
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  • 128
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    Slater determinant from atomic form factors (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 1-5 
    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 electron densities and expectation values for several physical properties predicted by three single determinant wave functions for the beryllium atom are presented. The wave functions are the Hartree-Fock, the Best Density Matrix, and the X-ray fitted. The X-ray fitted electron density comes closest to reproducing the exact density for r 〈 8.0 a.u. and gives, in most cases, better values for the physical properties.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300102
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  • 129
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    Composite exciton-phonon states in molecular crystals (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 7-18 
    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 known that the diagonalization of the exciton-phonon Hamiltonian gives rise to the composite exciton-phonon energy states. Within the single phonon approximation, two different diagonalized Hamiltonians are obtained for 0-0 and 0-1 phonon transitions in pure molecular crystals. The resulting secular equations are solved, and analytical expressions for the energy eigenvalues corresponding to the two transitions are derived. The thermal broadening due to the composite exciton-phonon states interaction is also calculated at low temperatures, and the results agree with experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300103
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  • 130
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    Electron transport in condensed matter. A novel approach using quantum chemical methods (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 31-49 
    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 mixed valence hopping conductivity is reviewed and prepared in a way suitable for quantum chemical calculations. Metallic conductivity appears as a limit case, if the thermal barrier for electron transfer is approaching zero and the orbital contact between the electron exchanging subsystems is large enough for adiabatic transfer. The theory is exemplified by calculations on the molecular crystal model and a model for doped polyacetylene. In the latter case it is possible to explain the decreasing thermal barrier for increased concentration of doping molecules as due to increased interaction between these molecules through the polymer chain.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300106
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  • 131
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    Critical phenomena in isoelectronic diatomic sequences - the 14-electron sequence (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 51-75 
    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 theory of isoelectronic molecules which describes stable and metastable members of a sequence has been developed. To achieve this synthesis, it has been necessary to require that the total electronic energy surface E(R,Z,Z') for the sequence contain critical points - that is, values of the nuclear charges Z and Z' at which energy minimum, maximum [at Re(min) and Re(max)], and horizontal inflection points occur. For ground state sequences a primary physical source of these extreme points is the screened, coulombic repulsion of like-charged atomic centers in the diatomics. With this realization, we can write analytical forms that have the correct scaling behavior and which properly model the screened, coulombic repulsion for E along certain straight-line trajectories in the (Z,Z') plane. This leads to the observation that Re(max) values diverge logarithmically in λ-like transitions wherever the screened coulombic repulsion becomes small as the nuclear charges vary along those trajectories.At the horizontal inflection points the E surface contains A2 folds, as required by Thom's theorem for analytical surfaces containing one control parameter. Within the isoelectronic sequence molecular subgroups have been noted and explained in terms of the underlying atomic shell structures of the molecules' constituent atoms. Using input data for seven stable molecules together with the analytical surface selected for study, we have estimated the equilibrium bond distances Re(min), dissociation energies De(min), and harmonic force constants E(2)(min) for 18 other neutral and charged species.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300107
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  • 132
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    Structures and 1H-chemical shifts of conjugation deficient hydrocarbons (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 97-107 
    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 geometrical and electronic structures and the 1H-chemical shifts of some conjugation deficient hydrocarbons and their benzenoid isomers 1-3 which consist of two concentric perimeters have been studied by means of semiempirical procedures. Conclusions on the importance of macrocyclic annulenoid conjugation are drawn from the bond lengths pattern and the proton shifts in these compounds.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300110
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  • 133
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    Unified treatment of the electronic structure of organic conjugated polymers (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 109-118 
    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: Theoretical calculations for polaron-type defect structures on organic conjugated polymers are carried out by Green's function and transfer function formalism. Firstly, the renormalization concept is applied to mathematically convert the polymers PPP, PPY, and PTP to an equivalent (trans-PA)-like form. Then, it is shown that Green's functions and polaron wave functions are readily obtained from the equations for trans-PA by the appropriate substitution of the renormalized parameters. It is suggested that the existence of defects such as polarons or bipolarons could be invoked to provide a unified treatment of electric conduction in organic conjugated polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300111
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    The concept of the topological atom within the MO-LCAO approach. I. On the effective charge of an atom-in-molecule (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 119-126 
    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 new definition of the MO-LCAO effective atomic charge is proposed, based on the concept of the topo-logical atom A general equation for the MO-LCAO electron occupancy of a topological atom is derived. It is shown that the intuitively introduced Mulliken gross atomic population is in fact an approximation to the electron occupancy of the corresponding topological atom. An approximate semiempirical procedure for evaluating the effective charge and effective radius of the topological atom is discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300112
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  • 135
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    Ab initio theory of hydrogen bonding in vitamin B6 (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 127-136 
    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 MO computations have been carried out for the crystalline form of the B6 vitamin, pyridoxinium chloride. In the crystal, the pyridoxine is protonized to pyridoxinium, with the formation of a hydrogen bond N—H+ ⃛ Cl-. For an isolated molecule, the calculations predict a single potential well, with H+ placed close to Cl- at the minimum. When neighboring molecules are included in the calculations, a double well is formed, and the lower minimum occurs for the proton placed near the experimentally observed position, in the vicinity of the N atom.Mulliken populations, which depend on the proton position, are described.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300113
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    The electronic structure of low-lying excited states of two model systems of retinal (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 289-302 
    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: 2,4-pentadienal and 2,4,6,8-nonatetraenal were studied as simple model systems of retinal. Four kinds of CI were performed on low-lying excited states of 2,4-pentadienal by using a split valence basis set. The results show that MR SD π CI is not adequate for the π-π* state and the single excitation σπ CI is a good compromise between cost and effectiveness as far as singly excited states are concerned. This CI was applied to the bigger model system. All-trans and 11-cis forms of aldehyde, Schiff base, and protonated Schiff base of the model system were studied. A fairly large energy lowering of about 1 eV of the first allowed excited state (π → π*) occurs when the Schiff base is protonated for both all-trans and 11-cis forms.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300208
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  • 137
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    Unitary group approach to general system partitioning. II. U(n) matrix element evaluation in a composite basis (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 365-389 
    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 explicit segment level formalism is derived for the matrix elements of the U(n) generators in an arbitrary (multishell) composite basis. The results of this paper, which contain the usual (spin-independent) unitary calculus approach as a limiting case, yield a more powerful and versatile algorithm than the traditional (spin-independent) unitary group formalism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300305
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  • 138
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    Alternative derivation of perturbation expansions in the projection operator formalism (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 421-431 
    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 perturbation-theoretic expansions obtained from Löwdin's projection operator formalism are derived in a new way, using Kato's formulation of perturbation theory. Kato's approach provides a convenient alternative to diagrammatic techniques for obtaining eigenvalues and eigenvectors. Different normalization criteria imposable on the wave function are easily visualized in terms of the operator that yields the perturbed state vector when it acts upon the unperturbed wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300308
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  • 139
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    Masthead (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986) 
    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.560300201
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  • 140
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    The spin-projected Hartree-Fock method: Direct optimization schemes and stability conditions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 239-264 
    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 necessary theory to construct different direct orbital optimization schemes in the framework of the spin-projected Hartree-Fock (spin-PHF) method for systems with an even number of electrons and for the proper characterization of the pertinent spin-PHF solutions is developed using the formalism of second quantization. The treatment is based on a unitary transformation of a reference DODS (different orbitals for different spins) Slater determinant. The energy expectation value corresponding to the transformed DODS Slater determinant is expanded in a Taylor series about the reference DODS Slater determinant, including second-order terms. On the basis of this expansion we propose several direct iterative approaches to optimize the spin-PHF energy expectation value: for example, implementations of steepest descent and conjugated gradient techniques, and Newton-Raphson, Fletcher, and limited configuration interaction approaches. The analysis of the second-order term in the Taylor series expansion of the spin-PHF energy expectation value about a spin-PHF solution is used to define stability conditions for spin-PHF solutions. Explicit expressions are reported for all matrix elements between different spin-projected DODS Slater determinants appearing in the treatment.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300205
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    Erratum (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 303-304 
    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: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300209
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  • 142
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    Unitary group approach to general system partitioning. I. Calculation of U(n = n1 + n2): U(n1) × u(n2) reduced matrix elements and reduced wigner coefficients (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 327-363 
    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: This paper is the first in a series of two directed toward a unitary calculus for group-function-type approaches to the many-electron correlation problem. In this paper we present a complete derivation of the matrix elements of the U(n = n1 + n2) generators, for the representations approapriate to many-electron systems, in a basis symmetry adapted to the subgroup U(n1) × U(n2). Explicit formulae for the fundamental U(n):U(n1) × U(n2) reduced Wigner coefficients, which are needed for the general multishell problem, are also obtained. The symmetry properties of the reduced Wigner coefficients and reduced matrix elements are investigated, and a suitable phase convention is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300304
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  • 143
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    Ab initio scf and Ci study of the electronic structure of the trichlorine radical (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 413-420 
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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 SCF and CI calculations using a double-zeta plus polarization basis set have been carried out on the trichlorine radical Cl3 to determine its electronic structure. The minimum in energy is determined for a bent structure at a bond angle of 146° and bond lengths of 2.18 Å (SCF) or 2.22 Å (CI). At linear geometry a 2Πu state is found to be lowest, approximately 7 kcal above the bent minimum, followed by a 2∑g+ state, which is around 4 kcal higher. This situation suggests that already for low quantum numbers a complex vibrational pattern in the Cl3 infrared spectrum is to be expected due to spin-orbit coupling as well as coupling of electronic, vibrational, and rotational motion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300307
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  • 144
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    Semidiffuse states of diatomic molecules: Configuration interaction studies of the lowest 2∑+ and 2Δ states of NS, SiF, and CCI (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 449-449 
    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.560300313
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    On the stability of conjugated hydrocarbon ions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 203-218 
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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 consider the question of predicting the stability of hypothetical structures that are too large for ab initio calculations, too complex for simple MO calculations, and too few for reliable semiempirical SCF MO schemes. The problem is illustrated on a polycyclic conjugated cation having 21 carbon atoms. The analysis is general and applies to conjugated hydrocarbons and their ions for which it is not apparent whether they exhibit aromatic characteristics (and, if they do, to what extent). For the investigated polycyclic cation we find that to a large extent its aromatic components are cancelled by its antiaromatic components resulting in an essentially nonaromatic system. The analysis, which is based on close examination of various contributing conjugated circuits, allows one to examine the partial role of the individual Kekulé valence structures as well as to foretell the nature of both the positively and the negatively charged system. We conclude that the particular cation should be stable but represents a challenge as it would be a cation with a rather small resonance energy. In contrast, the corresponding anion is relatively stable and, at least from a theoretical point of view, is less interesting.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300720
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  • 146
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    Complex scaled local density calculations: A review of recent developments (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 253-269 
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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: In this paper we review some recent developments of complex scaled local density models for treating shape resonances. The present scattering model is based on the static exchange plus polarization approximation, where we have the possibility to formally include continuum electron exchange with just the uppermost bound orbital or with all target electrons. This theory is then tested on the well known 2P shape resonances in the Be- and Mg- metastable ions and the 2D shape resonance in the e- - Mg scattering system. From the above formulation of the scattering problem we calculate partial wave S-matrix or Green's function resonance poles that can be used to interpret structures due to shape resonances in the cross section. In this contribution, however, we limit the numerical investigation to the partial wave S-matrix pole information and its interpretation and connection to the shape resonance.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300724
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  • 147
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    A local density theory for dynamical correlation corrections to single particle excitations in semiconductors (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 299-311 
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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: It is well established that the local density approximation (LDA), which is used in a large majority of all solid state band structure studies, severely underestimates band gaps in nonmetals. Here we describe an extension to semiconductors of the local density theory for quasiparticle self-energies. In contrast to the standard Kohn-Sham procedure' that applies rigorously only to ground state properties, this is a theory for the single-particle-like excitations of semiconductors. This approach includes the energy dependence within a local-density-dependent self-energy that is evaluated in the GW-approximation of Hedin. The essential feature is the incorporation of the semiconducting gap into the screening of the Coulomb interaction, which results in an increased energy dependence of the exchange-correlation hole. The resulting theory gives results for silicon and diamond bandgaps and valence bandwidths that are typically within 5% of the experimental value. Similarly good results are obtained for the zincblende IV-IV compound SiC and III-V compound GaP. Results for the anomalous heavier semiconductors Ge and GaAs, for which LDA gives very small to vanishing gaps, will also be discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300728
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  • 148
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    The noble gas atoms as impurities in siliconWork partially supported by CNPq, CAPES, and FINEP (Brazilian agencies). (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 347-351 
    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: Ground state one-electron energies have been calculated for the substitutional and interstitial helium, neon, and argon impurities in silicon by use of the self-consistent-field multiple-scattering Xα method within the framework of the Watson-sphere-terminated molecular cluster model. The substitutional noble gas atoms are found to inhibit the rebonding of the first neighbor's dangling bonds through orthogonality repulsion. The interstitial nobel gas atoms induce empty shallow levels close to the bottom of the conduction band. We tentatively relate these levels to the emission bands observed for silicon crystals implanted with helium, neon, and argon.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300732
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  • 149
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    The band description of materials with localizing orbitalsWork supported by the U. S. Department of Energy, BES-Materials Sciences, under contract W-31-109-ENG-38. (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 377-392 
    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 theory is a form of many body theory that maps the problem onto an equivalent single particle-like system by limiting to the ground state (or some limited ensemble). So it should be surprising that this ground state theory could have any relevance whatsoever to the excitation properties of a material, and yet it does when used carefully! However, the most interesting materials involve active orbitals that are at least partially localized in space, and this has profound effects both on the ground state and the excitation spectrum. My long term interest is in Ce and actinide compounds, where the popular concerns are mixed valence, heavy fermions, and the various forms of magnetic transitions. Band structure calculations can give a great deal of information concerning the mechanisms and degree of the localization as will be shown by examples using the Ce and U Ll2 structured materials and the Ce cubic Laves phase materials. There are some difficulties due to an incomplete knowledge of the functions involved that causes an underestimate of the local character. This will be illustrated and discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300735
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  • 150
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    Gaussian wave-packet dynamics (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 471-481 
    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 time-dependent variational principle is applied to the manifold of Gaussian wave packets. The translational and spreading degrees of freedom are treated equally. Comparison is made with frozen Gaussian dynamics and with the exact Schrödinger dynamics.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300741
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  • 151
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    Transferability of atomic descriptions in molecules (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 671-684 
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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: In a previous paper we proposed a new electrostatic description of the molecular electronic density in terms of charges, dipoles, quadrupoles, octupoles, etc. In this paper we apply this analysis to some first members of alkanic, ethylenic, acetylenic, alcoholic, aldehyde, amine, and nitrile series. Results show the clear transferability of the atomic descriptions for chemically similar atoms as well as the remarkable sensitivity of the electronic density versus changes in the basis sets, pointed out in our previous work. We discuss the calculation of molecular potentials from these atomic descriptions (and present an example) and some practical applications.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560300510
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  • 152
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    Announcement (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 715-715 
    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.560300514
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  • 153
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    Quantitative measures of similarity between pharmacologically active compounds (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 763-768 
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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 theoretical measure of molecular similarity based on ab initio computations of electron density derived from molecular orbital wave functions is first applied to a model series (CH3CH2CH3, CH3OCH3, and CH3SCH3) and then to the rings in a series of prostaglandins and to some histamine H2 antagonists. Comparison in terms of valence electron density seems to be a good basis for structure-activity studies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300605
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  • 154
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    On the construction of the effective pair correlation function with the fixed zero value at the points where two electron positions coincide (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 791-797 
    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 effective pair correlation function g̃(N)(r1;r2) accounting for the contribution of the kinetic energy functional to the electron correlation energy has been constructed. This function possesses the asymptotic property g̃(N)(r1;r2) = 0 at r1 = r2 and provides an efficient formalism for a model description of the electron correlation in many-electron systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300608
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  • 155
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    From determinants to spin eigenfunctions - a simple algorithm (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 799-807 
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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: Calculation of blocks of matrix elements between determinants associated with two fixed orbital configurations is very easy. A simple method to obtain the whole blocks and then transform them to the spinadapted basis is described. The method is suitable for many-particle operators, the number of operations to obtain matrix elements being independent of the number of orbitals or electrons. Some applications of the proposed algorithm, and possible extensions to eigenfunctions of Ľ2 and other operators, are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300609
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  • 156
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    Atomic Thomas-Fermi theory and electron subshell filling (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 831-844 
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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: In previous work on electron subshell filling, the existence condition of the integrals involved has not been taken into proper account. As a result, part of the calculated subshell occupation numbers is meaningless.In Theis' theory [9] the average number of electrons in a subshell is calculated as the difference between two integrals. With each of these integrals an existence condition is associated. Because of this, the number of electrons with angular momentum quantum number l can only be calculated for atoms of which the Z value is (much) larger than the corresponding empirical first-appearance Z value. Thus, the range of Z for which such numbers can be calculated, is restricted considerably, especially for larger values of l.Results obtained from a normalized version of Mason's approximation [13] to the exact Thomas-Fermi function, have been compared with a least-squares fit of the empirical subshell occupation numbers, and these are found to be as good as one may expect from a statistical theory.A lower bound to each of the empirical first-appearance Z values has been calculated. The results agree well with those reported in other work.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300612
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  • 157
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    On some solved and unsolved problems of chemical graph theoryDedicated to the memory of Professor Massimo Simonetta, an early contributor to Mathematical Chemistry. (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 699-742 
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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 development of several novel graph theoretical concepts and their applications in different branches of chemistry are reviewed. After a few introductory remarks we follow with an outline of selected important graph theoretical invariants, introducing some new results and indicating some open problems. We continue with discussing the problem of graph characterization and construction of graphs of chemical interest, with a particular emphasis on large systems. Finally we consider various problems and difficulties associated with special subgraphs, including subgraphs representing Kekulé valence structures. The paper ends with a brief review of structure-property and structure-activity correlations, the topic which is one of prime motivations for application of graph theory to chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300762
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  • 158
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    Momentum space approach to the relativistic atomic structure calculations (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 109-117 
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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 simple and straightforward derivation of the relativistic “no-pair” equation in momentum space is given for hydrogenic species. This is achieved by starting with a QED Hamiltonian in momentum representation and making a rigorous reduction into a system that contains a single electron but no positrons. The integral equation was solved for a series of hydrogenic systems using the Kwon-Tabakin-Lande technique. Numerical results were compared with those recently obtained by Hess, who employed the basis set expansion technique to solve the no-pair equation in configuration space.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300713
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  • 159
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    The difluoroethylenes: A reconsideration of the “Cis effect” (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 61-72 
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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 molecular orbital calculations have been carried out on all three isomers of difluoroethylene with geometry optimization. The calculations were done with a “double-zeta” basis set. After correction of the SCF energies for the effect of electron correlation, the 1,1-isomer is shown to be 8 kcal/mole lower in energy than the cis, which is 1 kcal/mole more stable than the trans. As the stabilization of the isomers increases, the distance between the fluorine atoms decreases: trans, 3.57 Å; cis, 2.77 Å; 1,1-isomer 2.20 Å. A simple explanation for these trends is based upon electrostatics and the small size and high electronegativity of the fluorine atom. As the fluorine atoms come closer together, the destabilization due to nuclear repulsions and electron repulsions is offset by the increased stabilizing electrons-nuclei attractions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290107
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  • 160
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    On the relationship between the electron-pair distribution function and the correlation energy of an atom (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1-9 
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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 pair distribution function h(r12;r1, γ) and the virial theorem are used to derive a general expression for the local contributions to the total correlation energy of an atom. A direct link between correlation effects and the correlation energy is obtained by use of G(r1, γ) and Γ(r1, y). The former is the probability associated with a given choice of r1 and γ, while the latter describes the local contribution to the correlation energy. Explicit calculations for the ground state of helium indicate that the angular dependence of the local contribution to the correlation energy is essentially independent of r1, whereas the local correlation energy shows a strong r1 dependence. The maximum contribution to the correlation energy occurs at intermediate values of γ where there is close agreement between the Hartree-Fock and exact densities.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290102
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  • 161
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    Correlation contributions to the radical cation states of linear even polyenes: An open-shell RHF-CNDO/S(CI) analysis of the optical and photoelectron spectra (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 35-60 
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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: Configuration interaction wave functions are calculated for the low-lying radical cation states of trans-butadiene, hexatriene, and octatetraene within the open-shell RHF-CNDO/S(CI) approach. The consequences of various one-electron contributions to the interpretation of existing photoemission and radical cation optical spectra are emphasized. Electron correlation is shown to be essential to achieve adequate energy and intensity profiles assuming photoelectron or optical excitation. The excitation energies and transition amplitudes (optical and photoemission) are also found to be sensitive to the molecular geometry. The present results are consistent with previous interpretations that photoionization measurements probe the neutralmolecule alternating single-double bond-length structure, whereas optical excitation samples an ion-state-state-induced “relaxed” reference configuration having a weakened bond-length alternation. Calculated trends in the spectroscopic properties are extrapolated to extended members of the even-polyene series.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290106
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  • 162
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    Intermolecular interactions: Elaboration on an additive procedure including an explicit charge-transfer contribution (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 101-118 
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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 additive procedure is derived for the computation of intermolecular interactions, in which an explicit expression for the charge-transfer energy contribution ECT is implemented. In the total interaction energy, \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta E = E_{{\rm MTP}} + E_{{\rm pol}} + E_{{\rm CT}} + E_{{\rm disp}} + E_{{\rm rep}}, $$ \end{document} the electrostatic terms EMTP and Epol are calculated as in our previous treatment. The dispersion contribution is calibrated by reference to variation-perturbation computations on model systems and the repulsion contribution is computed as a sum of bond - bond, bond - lone pair, and lone pair - lone pair interactions. Tests of the procedure are given for representative hydrogen-bonded systems.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290110
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  • 163
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    The quantum mechanical many-body problem in hyperspherical coordinates. Analysis of systems with coulomb interactions in terms of many-dimensional hydrogen-like wave functions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 129-147 
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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 method is described for using many-dimensional hydrogen-like wave functions as a starting point for constructing solutions to the Schrödinger equation of an N-particle system. The solutions are built up from symmetry-adapted hyperspherical harmonics, multiplied by functions of the hyperradius, r. Approximate asymptotic solutions for large values of r are discussed, as well as approximate solutions valid near r = 0. Properties of hyperspherical harmonics are discussed. General methods are presented for resolving arbitrary functions into hyperspherical harmonics and for constructing simultaneous eigenfunctions of generalized angular momentum and total orbital angular momentum.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290112
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  • 164
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    Editorial Comments (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. ix 
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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.560290204
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  • 165
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    The exact one-electron model of molecular structure (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 197-204 
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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 Schrödinger equation satisfied by the electron density is derived without approximation from the theory of marginal and conditional amplitudes. The equation arises from a factorization of the total N-electron wavefunction defined by the normalization appropriate to a conditional amplitude. This Schrödinger equation is an exact dynamical model for computing effective one-electron potentials from known N-electron wavefunctions. Results are presented for several small molecules. They display the shell structure of atoms, and the valence structure of both ionic and covalent molecules.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290209
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  • 166
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    Study of photoelectron spectra of some XPY3 molecules (X = O, S and Y = Cl, Br) by the SCF-Xα-SW method (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 393-397 
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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: In this paper we extend our previous studies to investigate the ionization energies of some XPY3 molecules (X = O, S and Y = Cl, Br). The calculated orbital energies agree very well with reported experimental ionization energies. The molecular orbital orderings obtained coincide with recent experimental orbital assignments. The results are also compared with previous ab initio and semiempirical calculations for OPCl3, OPBr3, SPCl3, and SPBr3 molecules. The comparison indicates that the present results show improved agreement with experiment and clarify certain ambiguities in the earlier assignments.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290313
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    Reality and complexity in asymptotic expansions for eigenvalues and eigenfunctions, with application to the JWKB connection-formula problem (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 261-272 
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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: Asymptotic expansions occur widely in quantum physics. The Rayleigh-Schrödinger perturbation theory for hydrogen in an electrostatic field (the LoSurdo - Stark effect) is one example. The 1/R expansion for the hydrogen molecule ion H+2 is a second. The quantum defect theory and the JWKB method are two more. It is not so widely known that the sum of such real asymptotic expansions may be complex, while the sum of complex asymptotic expansions may be real. The key to this nonintuitive behavior is Borel summation. By examining a simple example related to the exponential integral, the nature of this real-iscomplex, complex-is-real phenomenon is made simple. Then special application is made to derive and clarify the connection formulas (to all orders) in the JWKB method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290216
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  • 168
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    Double coset for symmetry orbitals (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 293-303 
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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: In this paper it is shown that, by use of the double coset decompositions of the point symmetry group and permutation group, the related symmetry coefficients and Clebsch-Gordan coefficients can be given in close formulas.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290302
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  • 169
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    Conformational behavior of azabiphenyls (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 541-551 
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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 conformational behavior of biphenyl-like compounds constituted by benzene and/or azabenzenes has been investigated at the STO-3G Hartree-Fock level. Although the STO-3G basis set probably overstimates conjugative attraction, it seems able to provide reliable general trends. In this connection the analysis of over 30 molecules shows that compounds with the same ortho substituents (including nitrogen lone pairs) have very similar conformational behavior, irrespective of their composition. Furthermore, the comparison of different isomers shows that repulsive interactions decrease in the order hydrogen-hydrogen 〉 lone pair - lone pair 〉 hydrogen lone pair. Conjugative, electrostatic, and steric interactions have also been expressed by well known semiempirical functions, thus allowing a better analysis of the overall torsional potential.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290326
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    On the excitonic nature of the first UV absorption peak in polyene (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 469-476 
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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 first absorption peak in the UV spectrum of polyene is interpreted in terms of charge transfer excitons. The exciton spectrum has been calculated from first principles using the Green's function formalism of charge transfer exciton theory. Electron correlation effects on the polyene band structure have been included with the help of second order Møller-Plesset perturbation theory and of the electron polaron model of Toyozawa. The spectrum of bound singlet excitons starts at EK=0 = 1.86 eV above the top of the valence band. A deeper lying triplet level is observed at 0.72 eV. Further correlation effects on the band gap and dielectric screening of the electron-hole ineraction are discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290319
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  • 171
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    Optical properties of large molecules and clusters in the frenkel exciton picture (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 497-510 
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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: Frenkel exciton theory is reviewed. This theory yields general formulas relating the absorption and circular dichroism spectra of large molecules or clusters to the optical properties of their subunits. It is shown that for weakly interacting systems, the circular dichroism associated with a band of exciton states is proportional to tr(FH), where F is an “optical matrix” constructed from the positions and transition dipole moments of the subunits, and H is an interaction-energy matrix. It is shown that if a system expnds isotropically, then tr(FH) falls off as the inverse square of the linear dimensions. This result is compared with experimental measurements of the low-temperature optical rotatory dispersion of proteins as a function of temperature. The optical properties of helical polymers are also discussed as a function of their geometrical parameters.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290322
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    Synchronism in the Diels-Alder reaction (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 511-518 
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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: Defined as the formation of two new bonds of equal length at the same time, synchronism has been shown to be not possible for the Diels-Alder reaction when the products are not of strict Cs symmetry. This has been done in two steps. First, the SCF-MO transition-state structures for the cyclization reactions of ethylene with cyclopentadiene and furan have been calculated. The activation energies (and heat of reaction) with the STO-3G, 3-21G, and 4-31G basis sets are as follows: with cyclopentadiene 35.0 (-80.7), 30.0 (-32.0), 38.4 (-19.9) kcal/mol; with furan 33.4 (-66.4), 34.6 (-16.5), 42.1 (-8.8) kcal/mol. Then, using a bond-order-bond-length relationship, a value for the tendency toward asynchronism has been calculated for substituted reactants where the two new bonds are arbitrarily held equal. This tendency has been shown in all cases which break strict Cs symmetry. Further, inspection of the atomic-orbital coefficients showed that the substituents cannot be considered as mere perturbations on the pi system in many cases.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290323
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    Classical and quantum mechanical calculations of conformational probability density distributions. Two-rotor molecules (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 553-562 
    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 study the dynamical structure of a two-rotor molecule, such as acetone, as a function of temperature, conformational probability density distributions are computed by using three different approaches: the so-called current approach, the classical approach, and the quantum mechanical oscillator approach. It is found that the three procedures yield comparable results, at least at normal temperature (25°C), although the current and, especially, the classical approaches give rise to too sharp distributions when compared with the quantum mechanical results. Owing to its simplicity, the current approach may be used advantageously, and it is easily extendible to many-rotor systems. Finally, it is verified that deuteration does not affect appreciably the conformation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290327
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    Weak intermolecular interactions: Statics and dynamics (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 663-676 
    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: This contribution consists of four parts: energy calculations, physical (mainly spectroscopic) characteristics, and static and dynamic aspects of interactions leading to the formation of van der Waals species.The main, first, part includes specific comments on computational procedures for systems of different size ([number of atoms, number of electrons]: small [4, 10], medium [dozens, hundreds], large [103, 104]) and colloid systems (considering also supermolecular structures). Rigorous and simplified methods of molecular quantum mechanics can be used with the first and second groups, respectively; for larger systems, only empirical potentials and the methods of the physics of a continuum are available. The transferability of empirical potential parameters is critically examined. The role of temperature, Gibbs energy, and entropy is mentioned together with the ensemble theory. The search for stationary points on potential energy surfaces (PES) and analytical fits to PES are reviewed briefly.The second part is an outline of what is expected from computational chemistry to meet the needs of spectroscopists. The third section deals with selection rules, equilibria and the rates of processes involving van der Waals species, and the role of these species in common chemical reactivity. The crucial role of entropy is mentioned in connection with hydrophobic phenomena, entropy-driven processes, and partitioning of substances between water and a nonpolar phase.In the final section, the role of computer experiments (molecular dynamics, Monte Carlo) is pointed out. Some shortcomings and promising features of these techniques are summarized.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560290409
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  • 175
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    The bonding properties of Mo—Fe—s clusters (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 701-715 
    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 paper the electronic structure of a series of Mo—Fe—S cluster compounds (from dinuclear to nonanuclear) are calculated by using the MAD-SCC and EH methods. The MO character, bonding property, as well as some other physicochemical properties are discussed. Some common regularities of these cluster compounds have been revealed. An extensive electron delocalization has been found in all these types of cluster compounds. There exists a certain degree of M—M bonding in each type of the clusters. The Mülliken bond order of the M—M bond are found to be as follows: Mo—Mo 〉 Mo—Fe 〉 Fe—Fe, and for remaining bonds: Mo—L 〉 Mo—Sb 〉 Fe—Sb 〉 Fe—L 〉 M—M. The chief contribution to the formation of stable Mo—Fe—S clusters is found to arise from the bonding interaction between the inorganic sulfur S* and metal atoms. The calculated results show that the rhomb is the basic structural unit in the Mo—Fe—S clusters. It is suggested that in the process of spontaneous assembly, the electron can be transported from the S* to the M atom, therefore the bridging effect of the S* plays an important role in this process.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290412
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    Semidiffuse states of diatomic molecules: Configuration interaction studies of the lowest 2Σ+ and 2Δ states of NS, SiF, and CCl (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 755-766 
    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 has been shown by ab initio configuration-interaction methods that the lowest 2Σ+ states of NS and SiF are ‘semidiffuse’ states, like the B 2Σ+ state of PO. The lowest 2Σ+ state of CCl also appears to be semidiffuse, although here the situation is not so clear. Semidiffuse states require diffuse orbitals in the wavefunction, but they are not Rydberg states. The second 2Σ+ state of each molecule is shown to be the lowest ns Rydberg state, whereas the third 2Σ+ state is a valence state for NS and CCl, and a 4po Rydberg state for SiF. The lowest 2δ state of each molecule derives from the 7σ → 3π valence configuration. Comparison with available experimental information shows, in general, good agreement.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290415
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    Prediction of new materials and properties of solids (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 843-854 
    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 total-energy pseudopotential method is described, and some applications are presented with emphasis on the predictive nature of the approach. For several applications, silicon is used as a prototype material, and the successful predictions related to structure and superconductivity at high pressure are discussed.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290422
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  • 178
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    Factors influencing proton positions in biomolecules (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 817-827 
    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 of quantum mechanical calculations are presented that suggest a number of mechanisms whereby protons may be shifted from one group to another along an H bond. The first factor to be considered is a stretching of the bond that drastically raises the energy barrier to transfer. It is possible to predict barriers for an arbitrary system based only on results for a simple system and knowledge of the relevant bond length in the isolated subsystems. Factors that increase the intrinsic basicity of the B group in A-H-B lead not only to a lowering of the energy of the A-HB state relative to AH-B but also to a reduction in the barrier to transfer of the proton from A to B. Ions in the vicinity of the H bond exert a powerful influence and can shift the proton to the less basic group across a gradient of several pK units. Rather than shielding the proton from the external ion, the H bond acts instead to amplify the effects of the electric field. Reorientation of the A and B groups relative to one another, i.e., bends of the H bond, also produce surprisingly large changes in the relative energies of the AH-B and A-HB states. Such bends are capable of pushing the proton across to the normally less basic group, providing a mechanism of coupling conformational changes to proton ‘pumping’ activity. It is found that the high and low pH states of a given H bond can have dramatically differnt relative populations of the AH-B and A-HB configurations. These observations are explained in terms of fundamental concepts involving electrostatic interaction energies.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290420
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  • 179
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    Theoretical interpretation of infrared spectra of the Cl—H stretching vibration in the gaseous (Ch3)2O · · · HCl complex (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 855-865 
    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
    Notes: The paper presents a theoretical interpretation of the fine structure of infrared spectra of the Cl—H stretching region in the gaseous (CH3)2O ··· HCl complex. The idea of Millen and Schrems is adopted, in which the spectrum represents a vibrational progression of the hydrogen-bond stretching mode, and each subband is formed by the progression of the hydrogen-bond bending mode. The rotational structure is present in such defined fine bands. Theoretical bands are calculated for three different temperatures and for the complex with DCl using two coupling parameters evaluated from the bandwidth. Results show that the most intense peak is associated with the Oσ ← Oσ transition in the stretching O ··· Cl vibration. They also suggest that the complex is nonplanar.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290423
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    The lower valence states of linear polyenes: Locations and identifications (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 875-881 
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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 experimental transition energy to the valence Ag state of butadiene is used to validate a subset of the theoretical calculations that have been carried out on this molecule. The validated calculated Ag transition energies of these calculations are then compared with the experimental Bu transition energies to determine the relative state ordering in isolated, unsubstituted butadiene, hexatriene, and octatetraene. The Ag origins are concluded to lie below the Bu origins for all polyenes except butadiene. Experimental confirmation of this conclusion is presented. The extreme breadth of the Ag transition, 1.0 eV, is noted. Some possible implications of this breadth are discussed.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290425
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    Multiple bonds and re(4f) binding energies of some rhenium halides (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 993-999 
    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: Experimental results on the bombardment of some rhenium trihalides by argon ions in a photoelectron spectrometer have yielded lower-valency rhenium halides. The presence of the compounds have been made evident by the destabilization of the Re(4f) and the relative decrease in the halogen spectral line intensities. A theoretical approach to the energy of the Re(4f) states have been studied by the MS X-α method. The molecular model used in the calculations is made up of rhenium polyhalides in D4h symmetry having the structure Re2Xn-8 (n = 2, 4, 6). A discussion is also presented on the formation of multiple bonds as a result of the overlap between the dxy orbitals of rhenium.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290434
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    Masthead (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986) 
    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.560290501
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    Laser and magnetic resonance propagators (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1139-1146 
    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: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290512
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  • 184
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    Atomic partitioning of two-center potentials for slater basis (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1155-1164 
    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 a previous paper we have shown that the long-range potential generated by the two-center distributions can be written as a sum of two multipolar expansions centered at the terminal atoms and defined so that the two series of multipoles be minimal. In this paper we show that both charge distributions and short-range potentials can also be separated in atomic contributions in a way consistent with the above mentioned partition of the long-range potentials.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290514
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    The basis set dependence of structures and energies of various states of cyclodisiloxane (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1191-1208 
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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: Several common basis sets, ranging from minimal to double-zeta, are applied to study the neutral singlet and triplet as well as positive- and negative-ion doublet states of cyclodisiloxane. The effect of d-polarization function exponents on the equilibrium geometries and energies is analyzed. The d-type functions seem to be essential in the basis set of silicon, whereas their presence on oxygen is less critical. The optimum exponents (with respect to SCF energy) are determined to be 0.45 for Si and 0.60 for O, very close to those recommended for the 6-31G** basis set. The best structural predictions are obtained with the 6-31G(2d, p) basis set, which contains two sets of d functions on the heavy atoms. The predicted Si—O bond length is 166 pm; the Si—Si and O—O distances are 237 and 232 pm, respectively, which correspond to an O - Si—O angle of 88.6°. The ground state is found to be a singlet. All higher states have longer Si—O bonds and Si - Si distances, whereas O - O distances are shorter. The energy separation between the singlet and other states is modified by electron correlation (MP treatment) by only a few kcal/mol.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290518
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    Accurate local-space treatment of hydrogen bonding in large systems (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1209-1222 
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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: Tests of the local-space approximation for electronic structure are carried out on a variety of hydrogenbonded systems. Regardless of size they are all found to be well localized in the sense of this approximation. For a local space defined by the valence atomic orbitals on X—H ··· Y, one obtains a bond energy within 6% of the “exact” full-space value. The potential energy surface and the electronic charge distribution are also accurately determined. In contrast with cluster models the local-space approximation satisfactorily accounts for long-range electrostatic and polarization effects.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290519
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    Is the self energy proportional to electronic relaxation? (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1277-1282 
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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
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290524
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    Two particle transition density and two particle bond order and their applications to electronic energy shifts caused by two particle interactions via geometric deformations (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1291-1302 
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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 concept of two particle transition density (TPTD) and two particle bond order (TPBO) is introduced and formally developed in order to extend the considerations of Callis, Scott, and Albrecht [1] to two particle interactions. These interactions may become important if the TPTD (TPBO) for one particle effects is small or the perturbation considered is essentially a two particle perturbation. As an example the geometric deformation of annulene perimeters is studied in detail. This deformation can be interpreted as a two particle perturbation because one particle effects do not contribute considerably. As a result of the perturbation characteristic energy shifts of the four lowest electronic singlet excitations depending on the type of deformation can be observed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290526
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    Some new aspects of bonding in cyclopropane (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1147-1154 
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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 peculiar properties of the three-membered ring in cyclopropane are partially due to characteristic relaxation effects of the carbon orbitals in the molecule. AO contraction in the two strongly C—C bonding MO's of A'1 type is essential for the stability of the C3 ring, whereas AO expansion in the E'-type HOMO contributes to the π character of the peripheral C—C bonds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290513
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    Strong nonadiabatic effects in reactions of photoisomerization (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1429-1435 
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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: Reactions of photoisomerization proceeding through a “funnel” are discussed (Fig. 1a, θ ≅ θ*, where θ is the angle of isomerization). Strong nonadiabatic interactions in the region of conical intersection of the multidimensional adiabatic potentials Us and Us0 are supposed to be responsible for the ultrafast nonradiative transition S1θ* → K2 S0 (K2 ≅ 1010-1012 s-1). The K2 dependence on the solvent viscosity (isomerization of t-stilbene in series ethanol--octanol) and polarity (isomerization of cyanine dyes in polar solvents) was determined to be in a good agreement with experiments.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290535
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  • 191
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    Theory of half-collision cross sections (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1483-1492 
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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: Standard Lippmann-Schwinger theory does not apply to decay of metastable or unstable states due to failure of the adiabatic hypothesis. In the Fock-Tani representation, discrete unstable states can be described by state vectors orthogonal to the asymptotic states representing their decay fragments, and a decay/formation interaction is exhibited explicitly as a portion of the total interaction Hamiltonian. This allows a straightforward derivation of a generalized Lippmann-Schwinger “half-collision” differential decay cross section without the need of projection operators. It reduces in first order to the product of a resonance line shape by a Golden Rule matrix element squared. In the general case the line shape is non-Lorentzian and the matrix element factor contains final-state interaction contributions. The exact expression is expected to be applicable to a variety of processes such as predissociation, autoionization, and Auger effect. The derivation employs the van Hove resolvent formalism to exhibit the dependence of the cross section on the complex self energy of the decaying state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290539
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    Free energy simulations: Applications to the study of liquid water, hydrophobic interactions and solvent effects on conformational stabilityReprinted from Proc. Int. Symp. Biomol. Struct. Interactions, Suppl. J. Biosci. 8 (192), 167-178 (1985). (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1513-1523 
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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: Free energy simulations using the Metropolis Monte Carlo method and the coupling parameter approach with umbrella sampling are described for several problems of interest in structural biochemistry: the liquid water, the hydrophobic interaction of alkyl and phenyl groups in water, and solvent effects on the conformational stability of the alanine dipeptide and the dimethyl phosphate anion in water. Proximity analysis of the results is employed to identify stabilizing factors. Implications of the result with respect to the structural chemistry of proteins and nucleic acids is considered.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290542
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  • 193
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    On the pressure dependence of the muon spin polarization in mixtures of noble gases (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1493-1502 
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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: In muon spin rotation (μSR) experiments, where spin-polarized positive muons are stopped in condensed matter, three magnetically distinguishable chemical environments can be observed. That is, the Larmor frequencies associated with diamagnetic environments and two types of paramagnetic environments (muonium and radicals) can be resolved. The chemical identities of the latter two are distinct since their Larmor frequencies are distinct, whereas the chemical identities of the possible diamagnetic species are not determined by the Larmor frequency since chemical shifts can not be resolved in μSR experiments. However, two different diamagnetic species have been observed in experiments performed on mixtures of noble gases. Their distinction arises through different thermal rate constants that lead to “fast” and “slow” relaxing components of the diamagnetic signal. The pressure dependencies of the amplitudes associated with these components are related to the stopping dynamics of muons in noble gas targets. A set of coupled rate equations for muon spin dynamics, based upon quantal Boltzmann equations, have been developed to describe this process in single component gases. This theory is now extended to mixtures. In particular, the dynamics of the muon spin is generated by the muonium hyperfine interaction and by time dependent rate constants for the various chemical species that are assumed to be present, namely, muonium and three diamagnetic species. Radicals have not yet been observed in low pressure gases. The coupled quantal rate equations are solved for two models of the stopping dynamics wherein the rates are taken as square box functions of time.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560290540
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    The electronic structure of 4H-pyran-4-one and its sulfur analogues (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1503-1512 
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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 electronic structure of 4-H-pyran-4-one and its sulfur analogues were studied using ab initio wave-functions. Bond lengths and overlap populations suggest low aromaticity for this group of compounds. Examination of Jorgensen plots of the lowest π orbitals of I--IV leads to the aromaticity order 4H-thiopyran-4-thione (IV) 〉 4H-thiopyran-4-one (II) 〉 4H-pyran-4-thione (III) 〉 4H-pyran-4-one (I). The effects of including d orbitals were studied using the 3-21G, 3-21G* (6d), and 3-21G* (5d) basis sets. Optimized bond lengths, vibrational frequencies, ionization energies, and dipole moments were also obtained, and results for different basis sets were compared.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290541
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    The theoretical approach to surface chemistry and heterogeneous catalysisInvited lecture at the Fifth International Congress on Quantum Chemistry, Montreal, Canada, August 18-24, 1985. (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1555-1560 
    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: Transition metals are the most interesting items among heavy atoms due to their extensive use in catalysis. Present understanding of heterogeneous catalytic reactions is still very poor, and new experimental and theoretical techniques have been developed in recent years with the aim of elucidating the mechanism of adsorption and reaction of simple molecules over metal surfaces or clusters. Empirical, semiempirical, and ab initio methods of calculations are briefly reviewed: results and perspectives are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290545
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  • 196
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    Etude MNDO des composes conjugues enneagonaux (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1599-1624 
    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 MNDO calculations of a series of nine-membered conjugated compounds. The geometries have been fully optimized. Cyclononatetraenyl and benzocyclononatetraenyl anions, nonapyrrol, and nonathiophene appear to be planar aromatic compounds. Following MNDO, nonafulvene has a planar prefered conformation, but a polyenic structure, while nonafuran and cyclononatetraene are gauche molecules. The Universal Huckel Method (UHM), a simple all valence electron empirical technique which describes σ systems using localized MO, gives, qualitatively, the same results as the MNDO method. The quantum calculation carried out with MNDO and UHM have been used to describe the physicochemical properties of ninememberedring conjugated compounds under consideration. To our knowledge, we present here the first theoretical study dealing with nine-membered conjugated molecules.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290549
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  • 197
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    Masthead (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986) 
    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.560290601
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  • 198
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    The omega function for the lithium atom (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1705-1712 
    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 omega model is reviewed in the case of a three-electron function and the omega function determined for the lithium atom ground state by using a procedure based on Brillouin' theorem. The resulting function is analyzed in terms of natural configurations, and the correlation coefficient determined as a function of the distance to the nucleus. It is found that the omega function is essentially equivalent to two configurations built up with the occupied NO' and that the model introduces mainly correlation at large distance. These results contrast with those obtained for the beryllium atom using the same model.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290604
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  • 199
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    Structural features of some small carbonyls in the 1,3nπ states: An mcscf study (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1745-1754 
    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: Structural features of a series of tetraatomic carbonyls in the 1,3nπ* states are studied by using a recently proposed MCSCF algorithm at the INDO/2 level. The computed geometrical parameters and the inversion barrier heights agree quite well with the available experimental or ab initio theoretical data. The calculated transition energies turn out to be somewhat lower than the experimental counterparts. The specific MCSCF algorithm used is found to have excellent convergence properties.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290607
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  • 200
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    Molecular valence calculations based on stepwise approximations for orthogonality and core-valence interactions (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1789-1797 
    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 approximate method for the calculation of the electronic structure of molecules has been developed. The principal approximations involve freezing of the atomic core orbitals, description of the core-valence interactions by density matrix expansion techniques, and the enforcement of the core-valence orthogonality by auxiliary bases and projection operator techniques. The general principle in the approximations is their stepwise execution. Each approximation can be separately relaxed and tested for reliability. The developed computational techniques have been described. A detailed analysis for the approximations is given for LiH. Other molecular test calculations include HCl, H2S, H2Se, and H2S2 molecules. The results demonstrate the suitability of the method for molecular studies.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290611
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