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  • 1985-1989  (406)
  • 1987  (406)
  • Computational Chemistry and Molecular Modeling  (406)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 339-343 
    ISSN: 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: Andrew Crowther Hurley was born in Melbourne, Australia, on 11 July 1926 and received his early education at Melbourne Church of England Grammar School. He graduated from the University of Melbourne with high honors in mathematics and natural philosophy and, in 1949, was awarded his M.A. with first class honors in the school of mathematics for his thesis “The Irreducible Crystal Classes in Four Dimensions,” his supervisor being Dr. Hans Schwerdtfeger. From 1950-1952 he was a member of Trinity College, Cambridge, and was awarded a Ph.D. for his research in theoretical chemistry under Sir John Lennard-Jones. In 1953 he returned to Melbourne and joined what was to become the Division of Chemical Physics of the Commonwealth Scientific and Industrial Research Organization (CSIRO). The award of a fellowship by Trinity College enabled him to spend two more years, 1954-1956, in the Theoretical Chemistry Department of the University of Cambridge, and this was followed by a year with Professor J.C. Slater's solid state and molecular theory group at the Massachusetts Institute of Technology. In 1957 Andrew again returned to the Division of Chemical Physics in Melbourne, where he has remained, except for the academic year 1962-1963, when he was Visiting Professor in Theoretical Chemistry at Iowa State University.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 361-368 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For exact few-particle wave functions the choice of expansion has a strong influence on the ease with which the coefficients may be determined. Some expansions, such as those involving hyperspherical coordinates, require complicated expressions for Coulomb interaction potentials. The choice of expansion provides a possible means for minimizing algebraic problems in determining the exact wave function. The complexity due to the nonseparable terms in the potential occurs at different stages of the solution of the Schrödinger equation when the expansion is transformed. When solving recurrence relations to determine the wave function, it is necessary to understand the relationship between degrees of freedom in the solution and the boundary conditions. The degrees of freedom in the solution must be chosen to ensure that the wave function is continuous and normalizable and that the derivatives are bounded everywhere.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 369-382 
    ISSN: 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 purely structural definition of aromaticity based on the average ring bond length and -bond order is proposed. The definition is illustrated for N-heterocycles by reference to theoretical STO-3G and 3-21G geometries and charges for some pteridine derivatives. The treatment focuses on the gross structural changes (i.e., ring size, overall degree of π-electron delocalization, and net ring charges), accompanying chemical changes, such as substitution, tautomerization, ring reduction, and deazination, as well as the structural interdependence of the two rings in a bicyclic ring system.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 383-391 
    ISSN: 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: Some of the problems, discussed recently, with the idea that every molecule has a structure can be removed by adopting the idea that some molecules have several structures with probabilities of transfer between them. This is supported theoretically by using diabatic energy surfaces and wave functions. Since these are not easy to define in general, their definition is given in the special case where the surfaces permute into one another. Two kinds of permutation operations are required. The analysis is given more fully for two intersecting diabatic surfaces. The analogy to the double-valued property of the wave function near a conical intersection is given.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 393-403 
    ISSN: 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 3-21G basis set shares with its older cousin, the 4-31G basis set, a tendency to overestimate valence angles at nitrogen atoms and to underestimate seriously barriers to inversion at such atoms. The 6-31G* basis set generally yields greatly improved results in these respects. It is here shown that, for a variety of molecules, supplementation of the 3-21G basis set at three- or two-coordinate nitrogen atoms with a set of six d-functions having exponent 1.0 leads to optimized geometries and inversion barriers at such nitrogen centers in good agreement with results obtained with the 6-31G* basis set. This supplemented basis set, designated as 3-21G(N*), also leads to calculated vibrational frequencies in good agreement with those calculated with the 6-31G* basis set. The 3-21G(N*) basis set offers an economical alternative to the 6-31G* basis set, particularly for molecules containing several first-row atoms other than nitrogen.
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 405-415 
    ISSN: 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: Binding of Zn2+ to imidazole (Im) and methyl imidazole (MeIm) is studied by ab initio methods as a model for the effect of cation binding on tautomeric energies. Gradient energy optimized conformations were obtained for all neutral and ionic structures, including the deprotonated molecules and the ylides. The N3—H tautomer of MeIm is calculated to be more stable than N1—H by about 1 kcal/mole. However, binding of a Zn2+ cation to the available nitrogen site is found to reverse the order of binding, leaving N1—H more stable by 1 kcal/mole. Binding of Zn2+ produces a significant perturbation in the electronic structure, a smaller shift in the equilibrium conformation of the imidazole ring, and only a small absolute shift in the relative tautomer energies. Methyl substitution at C5 has a small effect on both conformation and energetics.A high-energy ylide tautomer is produced by moving the proton bound to C2 to the N1 atom. The binding of Zn2+ to the C2 site is substantially stronger than to the N1 site, yielding nearly isoenergetic ZnIm2+ conformations for binding to either N or C atoms. For the deprotonated salts the lowest energy conformation has the C2—N3 bond bridged by Zn2+.
    Additional Material: 7 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 417-424 
    ISSN: 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: Pair coupling between a chiral molecule and an achiral molecule can induce weak circular dichroism in the achiral partner, as is well known in induced circular dichroism. Here the effect of the same coupling on the chiral partner is analyzed. The effect is an increase or decrease in the rotatory strength that may be detectable under conditions where the effect is enhanced by a near-resonance.
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 425-427 
    ISSN: 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 made clear that two different statements in the literature concerning energy derivatives are completely compatible by deriving them as two different interpretations of the same equation. Some other aspects of these results are also discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 435-443 
    ISSN: 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: Accurate methods for computing energies and electronic properties of atoms and molecules have been derived from direct treatment of localized pairs of electrons. The conceptual development and implementation of such methods is reviewed.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 429-433 
    ISSN: 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 greatest single success of modern computational quantum chemistry has been its ability to correctly predict the geometrical structures of molecules. The FOOF molecule stands in contrast to the overwhelming mass of comparisons between theory and experiment. This research shows that configuration interaction (CI) methods including all single and double excitations (SD) fail to predict the correct FOOF structure, even when high-quality basis sets are employed.
    Additional Material: 2 Tab.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 445-453 
    ISSN: 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 modified Bohr orbit procedure is used to calculate the energies for the 1S ground state and the 2P, 3D, and 4F excited states of the helium atom. The energies are calculated from \documentclass{article}\pagestyle{empty}\begin{document}$ {{\int\limits_0^\pi {E\left(\Phi \right)P\left(\Phi \right)d\Phi } } \mathord{\left/ {\vphantom {{\int\limits_0^\pi {E\left(\Phi \right)P\left(\Phi \right)d\Phi }} {\int\limits_0^\pi {P\left(\Phi \right)d\Phi } }}} \right. \kern-\nulldelimiterspace} {\int\limits_0^\pi {P\left(\Phi \right)d\Phi } }} $\end{document}, in which E(φ) is the Bohr orbit energy for angle φ between the position vectors \documentclass{article}\pagestyle{empty}\begin{document}$ \vec r_1 $\end{document} r1 and \documentclass{article}\pagestyle{empty}\begin{document}$ \vec r_2 $\end{document} r2, and P(φ) is a probability function for this angle. Numerical procedures are used to evaluate the integrals. Energies that range between -2.9082 and -2.9054 au are calculated for the 1S state (cf. -2.9037 au, exact). The Bohr energies for the excited states are -2.1318, -2.1240, -2.0562, -2.0555, -2.0314, and -2.0312 au, which are generally close to the exact energies of -2.1332, -2.1239, -2.0557, -2.0557, -2.0313, and -2.0313 au for the 23P, 21P, 33D, 31D, 43F and 41F states. Some relationships that exist between the Bohr theory and the Schrödinger local energies are discussed. Approximate Bohr orbit estimates for the energies of the 2P states of He, Li+,…,Ne8+ are reported.The invariance of the two-electron Bohr hamiltonian with respect to the interchange of the electron coordinates leads to two classical probability functions when the orbit quantum numbers for the two electrons differ.
    Additional Material: 4 Tab.
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 455-461 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problem of systematically coloring periodic patterns has interested textile designers, artists, and crystallographers since 1935. The classification of possible procedures has been seen to depend on space groups and their subgroups and factor groups. Crystallographers naturally worked in Euclidean three-space before generalizing to two, and then four, dimensions. The present treatment deals with the one-dimensional case in a manner that can easily be extended. Avoiding the crystallographers' customary emphasis on translations, among the various kinds of symmetry operations, allows the classification to be readily adapted to non-Euclidean geometries.
    Additional Material: 1 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 463-470 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Valence-bond calculations are reported for the isoelectronic series of molecules and ions: N2, CO, BF, NO+ and CN-. The most important structures are N≡N, C=O, Bπ—F, N+=O and C=N. Hybridization of the 2s and 2p orbitals is important. Only two or three structures are required to obtain an energy lower than that obtained with the molecular orbital approximation. Structures in which the electronegative element loses a σ-orbital or gains a π-orbital are favored. π-bonds tend to be favored over σ-bonds. The bond in NO+ resembles that in CO, whereas that in CN- resembles the bonding in N2.
    Additional Material: 5 Tab.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 471-487 
    ISSN: 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, CI, CEPA, and MCSCF techniques are compared and contrasted in a theoretical study of the 1s core ionized Li2 molecule from the point of view of core hole localization. In agreement with earlier studies of symmetric core ionized molecules, SCF theory is found to give a physically reasonable description of core ionization only when symmetry breaking is allowed. This results in a dramatic lowering of the energy of the core ionized state and hence of the ionization potential. By extension, CI wave functions that are developed in terms of a broken symmetry SCF reference plus its single and double excitations are found to perform significantly better than those constructed from symmetry adapted SCF orbitals. Alternatively, if the full point group symmetry is to be retained, a multiconfigurational treatment is called for and, in agreement with the conclusions of an analogous study on O2 [H. Ågren, P.S. Bagus, and B.O. Roos, Chem. Phys. Letters 82, 505(1981)], it is found that a modestly sized MCSCF wave function is capable of accounting for the energetic effects of symmetry breaking. Potential energy curves for Li2 and several states of core ionized Li2 have been calculated, allowing predictions of the adiabatic ionization potential and vibrational, satellite, and Auger structures in the photoelectron spectrum of Li2 to be made.
    Additional Material: 4 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 489-505 
    ISSN: 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 practical algorithm is described for generating a set of symmetry- and spin-adapted antisymmetrized products of molecular orbitals (SAAPs) which form an orthogonal basis for a full active configuration space. The spin-adaptation is completely general. The space-symmetry adaptation is accomplished for the groups C∞v and D∞v.
    Additional Material: 4 Tab.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 507-520 
    ISSN: 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: Multireference configuration interaction (MR-CI) calculations using energy-selected and complete-active-space reference configurations are compared for a large-basis-set treatment of the (H2)2 van der Waals complex in a T geometry. Procedures for estimating truncation errors arising from energy threshold selection of configuration state functions and for extrapolating to the full CI limit are tested by comparisons with untruncated calculations and with the full CI energy. The results of these tests show that great care is required in the use of the correction and extrapolation formulas. Optimization of the orbitals of the reference wave function (compared to the use of SCF orbitals) is found to produce order-of-magnitude improvement in the results.
    Additional Material: 5 Tab.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 521-534 
    ISSN: 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 increasing rate at which improvements in processing capacity outstrip improvements in input/output performance of large computers has led to recent attempts to bypass generation of a disk-based integral file. The “direct” SCF method of Almlöf and co-workers represents a very successful implementation of this approach. The present work is concerned with the extension of this general approach to CI and MCSCF calculations. After a discussion of the particular types of MO integrals for which  -  at least for most current generation machines  -  disk-based storage seems unavoidable, it is shown how all the necessary integrals can be obtained as matrix elements of Coulomb and exchange operators that can be calculated using a direct approach. Computational implementations of such a scheme are discussed.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 535-563 
    ISSN: 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 construct bases for the irreducible representations of the rotation group O(3) which are symmetry adapted to a Crystallographic point group. We obtain explicit expressions for the cubic groups, which are valid for arbitrary values of the angular momentum quantum number l. Our method yields an efficient algorithm for both analytical and numerical work. An explicit formula for the multiplicities of an irreducible representation for the cubic groups in an arbitrary angular momentum term l is also derived.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 20
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 565-567 
    ISSN: 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: Two-center Coulomb and hybrid integrals are combined into a single expression by use of the formulas given by the author for the expansion of real and complex STO's about a point displaced from the orbital center. The final results are expressed in terms of the overlap integrals between STO's. Analytical formulas for the evaluation of these integrals have been established recently by the author.
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 569-579 
    ISSN: 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: There is considerable evidence indicating that the primary in vivo DNA alkylation product of vinyl chloride, believed to be responsible for its carcinogenicity, is the 7-N-(2-oxoethyl) derivative of guanine. Using a representative keto-enol system, we have studied computationally two possible equilibria involving this adduct. The first is between the 2-oxoethyl derivatives of the keto and enol forms of the representative system, whereas the second is between the 2-oxoethyl derivative of the keto form and the corresponding hemiacetal. In the case of the analogous guanine derivatives, such equilibria could lead to disruption of the hydrogen bonding between guanine and cytosine in DNA and could cause miscoding and replicational and transcriptional errors. An ab initio self-consistent field molecular orbital study has been carried out using the GAUSSIAN 82 system of programs. Optimized structures and energies have been calculated at the 2-21G level for the representative keto-enol system and its 2-oxoethyl and hemiacetal forms. The formation of the 2-oxoethyl adduct was found to have no significant effect upon this keto-enol equilibrium, which strongly favors the keto form. Our calculations further show hemiacetal formation to be an unlikely possibility for this system. On the basis of these results and recent data on guanine tautomers, we speculate about the analogous equilibria involving the guanine derivatives.
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  • 22
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 581-590 
    ISSN: 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 spectral density operator technique is proved to be a convenient tool for derivation of approximate topological formulae for total pi-electron energy (Epi) of benzenoid hydrocarbons (BHs). Developed mathematical formalism points out a common origin of three different measures for the stability of BHs, namely: resonance energy (RE), number of Kekule structures (K) and HOMO-LUMO separation (XHL). In turn, a novel topological invariant corresponding to “normalized” RE is derived. Numerical calculations for a representative set of BHs demonstrate effectiveness of the present approach. Various approaches to an estimation of BH stabilities are discussed.
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  • 23
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 591-603 
    ISSN: 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 CI space Xn generated by n electrons moving over 2n spin orbitals is considered. It is shown that the transitions between different eigenstates ψi ∊ Xn of alternant and weakly alternant Hamiltonians are governed by some special selection rules. These selection rules are characteristic to alternant systems, and they do not apply to nonalternant systems. The set of all such selection rules can be easily derived from the splitting theorem. In particular, the selection rules associated with spin independent alternant systems are considered. As an example, the PPP Hamiltonian Ĥp describing netural alternant hydrocarbons is treated. In the case of electron dipole transitions between eigenstates ψi ∊ Xn of the Hamiltonian Ĥp, the selection rules obtained are in agreement with the selection rules derived previously by Pariser and McLachlan.
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  • 24
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 605-609 
    ISSN: 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 asymptotic formula describing a dependence of the algebraic structure count (ASC) of the even-membered rotagraphs on its size (N) is derived from the backfolding theorem for the electronic band structure. This new result imposes very strict constrains on ASC as a function of N.
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  • 25
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 639-647 
    ISSN: 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 the Xα method a generalized Hellmann-Feynman theorem has been derived, and its most important applications are presented. A formula for electronegativity using the definition of electronegativity given by Iczkowski and Margrave and the magnetic nuclear shielding factor and its relation to the electronegativity have been obtained. The virial theorem of the Xα method has also been derived with the aid of the Hellmann-Feynman theorem.
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  • 26
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 611-623 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational preferences of modified nucleic acid base N6-(N-glycylcarbonyl) adenine, gc6Ade, have been investigated using the quantum chemical PCILO (Perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually. The theoretically predicted most stable, minimum energy conformation of the molecule is such that the substituent on N(6) spreads away from the imidazole moiety of the adenine ring, thus keeping distal orientation. The preferred molecular orientation is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The carboxylic group of the substituent is trurned away in relation to N(11)H…N(1) and is perpendicular to the plane through the rest of the moleculeThe alternative stable conformation corresponding to an 0.8 kcal/mol higher energy has a coplanar carboxylic group turned towards the same side as N(11)H…N(1) and is exhibited in the crystal structure of the nucleoside derivative, gc6A. Energetically, the carboxyl group may change its orientation over a wide range, without much destabilization. This suggests probing by the carboxyl group of the molecular environment in the vicinity of the anticodon in tRNA.
    Additional Material: 6 Ill.
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  • 27
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 649-662 
    ISSN: 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: Energies and geometries for a number of small hydrogen bonded dimers have been calculated by semiempirical method based on a perturbation approach. Results have been compared with experimental and the best theoretical data. A quite good description of equilibrium configurations has been obtained in every case when local multipoles from sufficiently accurate wave functions have been used. Hydrogen bond lengths have not been predicted with sufficient precision. Results indicate, however, that it should be possible to achieve improvement in the framework of the applied calculation scheme by modification of the parameter values.
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  • 28
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 673-684 
    ISSN: 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 interative technique to solve nearly singular systems of linear equations of quantum chemical interest is described and tested. The solution is split into regular and singular parts, the last being the resonating eigenvector.
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  • 29
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    International Journal of Quantum Chemistry 31 (1987), S. 663-672 
    ISSN: 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: Iterative methods for computing eigenvalues and eigenvectors of large symmetric matrices are discussed using the language of multidimensional partitioning technique. New variants are proposed and found useful particularly for the computation of highly excited states of CI matrices.
    Additional Material: 3 Tab.
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  • 30
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    International Journal of Quantum Chemistry 31 (1987), S. 693-693 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 31
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    International Journal of Quantum Chemistry 31 (1987), S. 697-697 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 32
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    International Journal of Quantum Chemistry 31 (1987), S. 695-696 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 33
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    International Journal of Quantum Chemistry 31 (1987), S. 893-901 
    ISSN: 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 analytic expressions of the integral prototypes involving both Slater and s-type Gaussian functions, explicity derived in Ref. 1, are generalized to the case of higher order modified Gaussian functions [2].
    Additional Material: 1 Tab.
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  • 34
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    International Journal of Quantum Chemistry 32 (1987), S. 411-426 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report a model calculation of the transport of a local (site) excitation in a doped molecular crystal containing one impurity. We do not consider the impurity as a direct trap for electronic excitations (zero trap depth) but assume that exciton-phonon interaction is exclusively given by the coupling of excitons with the vibrational displacement of the impurity. The dynamical problem is solved by using a time-dependent effective potential consisting of equilibrium average exciton-phonon interaction and fluctuations around this average. Two correlation functions are computed using the slow phonon limit and assuming that the temperature of the system is 300 K.Transmission of the excitation energy over a distance of eight spacings takes place, electronically, within a few picoseconds. With the exciton-phonon interaction switched on, calculated correlation functions diminish very rapidly with increasing time, indicating that an irreversible transfer of excitonic energy to the thermal bath takes place. Thus transmission of the excitation energy over such a distance (and without a high rate of trapping) is not an efficient process.
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  • 35
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    International Journal of Quantum Chemistry 32 (1987), S. 435-450 
    ISSN: 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 locality of conformational state with relation to the asymmetry in potential is proved. The adequacy of harmonic approximation of conformation wave function is discussed. Then, on the grounds of the rigorous definition of the conformation-vibrational state, the role of vibration in the information transmission and cooperativity is discussed by the calculation of statistical mechanics. In the rest of this article, the conformational change as a quantum transition is investigated in detail. The viewpoint of conformational transition with respect to electronic motion is stressed. On the basis of proposed selection rules, the approach to the conformational change that consists if multiple steps is clarified.
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  • 36
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    International Journal of Quantum Chemistry 32 (1987), S. 551-562 
    ISSN: 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: Pair-excitation multiconfigurational self-consistent field (PEMCSCF) treatment of 11 small molecules (LiH, BeH2, BH3, BF, CH4, C2H4, C2H2, CH2O, NH3, H2O, and HF) has been carried out in a minimum basis set of Slater Transform Preuss functions as fitted by six cartesian gaussians (STP-6G). The advantages of accuracy without using a split basis are shown by comparison to familiar 4-31G and 6-31G calculations using molecular geometries optimized with STO-6G basis sets. A benefit is shown for the use of minimum basis fitted to STP functions: they overemphasize long-tail radial dependence to achieve long range basis sensitivity without increasing the basis size at the AO-to-MO transformation step in the configuration interaction portion of the MCSCF algorithm. Fully optimized STP-6G parameters are given and appear to be transferable as shown for acrolein. A FORTRAN listing of the full least squares fitting algorithm is available* for in situ generation of STP-6G orbitals energetically superior to 4-31G, or a less accurate STP-6G 1S, 2S, and 2P basis may be scaled directly as if they were STO-6G functions, but with considerably lower energy that with an STO-6G basis.
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  • 37
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    International Journal of Quantum Chemistry 32 (1987), S. 575-589 
    ISSN: 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 avoid the determination of the perturbed wave function in the susceptibility calculation of closed shell molecules, several authors have developed gauge-variation methods based on Rebane's work. The present work illustrates that introduction of a certain restriction in the gauge-variation method makes the susceptibility calculations exceptionally simple. The restriction involves the use of the Coulomb gauge so that the gauge-function satisfies Laplace's equation. The restriction was dictated by the demonstration of gauge-invariance of the Rayleigh-Schrouml;dinger perturbation theory of diamagnetism. The method with the prescribed restriction has been applied to the H2O molecule, as an example, to demonstrate the advantages.
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  • 38
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    International Journal of Quantum Chemistry 32 (1987), S. 591-594 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The time-dependent Schrouml;dinger equation for the oscillator H = α(t)p2 + β(t)x2 + γ(t)x is exactly solved. The time evolution operator is easily obtained by means of an operator algebra and the quantum-mechanical equations of motion. The problem is reduced to solving the classical equations of motion. The method is shown to apply to multidimensional oscillators.
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  • 39
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    International Journal of Quantum Chemistry 32 (1987) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 40
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    International Journal of Quantum Chemistry 32 (1987), S. 47-56 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometries of all 12 complexes in which HF, HCl, or HBr is paired with NH3, NMeH2, NMe2H, or NMe3 are optimized with the MINI-1 basis set. As the basicity of the amine is increased via progressive methylation, or as the proton affinity of the halide is diminished, the proton equilibrium position shifts toward the nitrogen, but in no case is this shift far enough to classify the complex as an ion pair. When the effects of a polarizable medium are included via the SCRF formalism, the shift of the proton toward the nitrogen is enhanced by increases in the solute-solvent interaction such that relatively modest coupling leads to complexes of ion-pair type. In all cases, complexes containing HBr are the most sensitive to either the basicity of the amine or the influence of the medium whereas the HF analogs are affected very little.
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  • 41
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    International Journal of Quantum Chemistry 32 (1987), S. 297-315 
    ISSN: 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 recently discovered a new entirely unexpected, and highly selective protein - ligand interaction. This new kind of molecular interaction was recognized by chromatography of proteins on divinylsulfonated agarose gels which had been deactivated using mercaptoethanol. The essential structure of the interacting immobilized ligand is quite simple and nonionic. It can be generally represented by: \documentclass{article}\pagestyle{empty}\begin{document}$$\hbox{agarose-O-CH}_2 \hbox{CH}_2\hbox{-SO}_2\hbox{-CH}_2\hbox{-X-}$$\end{document} where X was first a thioether but can also be N, O(S 〉 N ≫ O) or possibly any atom with at least one lone electron pair. We have provisionally termed peptides and proteins interacting with this ligand „thiophilic,“ in recognition of their affinity for the definitive thioether sulfone constituents. The thiophilic adsorption process is promoted by water-structuring or „antichaotropic“ salts such as sulfates or phosphates and would appear to be entropically driven. The thermodynamics of such a process are discussed relative to protein recognition of the immobilized thioether-sulfone ligand. We do not yet know the precise mechanism for the interaction but we believe that salt allows the protein into close contact with the immobilized thioether-sulfone group where short-range forces are likely to be important. Evidence suggests that aromatic side chains on the protein-binding site may be involved and we therefore expect that some kind of electron-donor-acceptor or proton-acceptor mechanism is likely involved. Two important applications of thiophilic adsorption are the selective immobilization of functional antibodies as well as purification of immunoglobulins from serem, ascites fluid, and hybridoma cell culture media. Monoclonal antibodies can be purified in one step under extremely mild (structure-stabilizing) conditions. We therefore consider the further characterization of thiophilic adsorption of major significance in the fields of immunology and biotechnology and hope that this presentation will inspire attempts to explain the interaction in terms of quantum chemistry.
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  • 42
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    International Journal of Quantum Chemistry 32 (1987), S. 573-587 
    ISSN: 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 quantum path integral molecular dynamics method was utilized to explore the compositional, structural, and size dependence of localization mode of an excess electron in ionic and hydrogen-bonded clusters, providing information on the nature of surface states and on isomerization induced by electron attachment in large finite systems.
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  • 43
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    International Journal of Quantum Chemistry 32 (1987), S. 589-593 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hybridization, bond, and deviation angles as well as strain energies in Archimedean carbon clusters C24, C48, C60, and C120 are calculated within the iterated maximum overlap approximation.
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  • 44
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    International Journal of Quantum Chemistry 31 (1987), S. 179-184 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 45
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    International Journal of Quantum Chemistry 31 (1987) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 46
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    International Journal of Quantum Chemistry 31 (1987), S. 187-194 
    ISSN: 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 was shown recently by the present author that the double symmetrization and the double antisymmetrization are essential in the spin-dependent and the spin-free formalisms, respectively, to perform the exclusion of all the unnecessary spin eigenfunctions and the selection of a unique set of linearly independent spin eigenfunctions. The double antisymmetrized Wigner matric basis and the Wigner double symmetrized matric basis are presented in this article for N up to 6. The double symmetrization or the double antisymmetrization also results in a direct expansion method for the calculation of the orthogonal spin coefficients; this direct method does not require the knowledge of the wave functions of the N - 1 electron system. The modified method of Graebenstetter can also be used to calculate these orthogonal spin coefficients.
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  • 47
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    International Journal of Quantum Chemistry 31 (1987), S. 243-249 
    ISSN: 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 algebra of the two-dimensional harmonic oscillator is exploited to obtain matrix elements between eigenstates of the Morse potential. This follows after mapping the latter into the radial equation of the former problem by means of a change of variable and the use of the angular variable as a dummy variable.
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  • 48
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    International Journal of Quantum Chemistry 31 (1987), S. 195-216 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular orbital calculations (MINDO/3) using energy minimized molecular geometries were performed on oxidized and reduced lumiflavin and related methylated isoalloxazines, including cationic and anionic species. Close agreement with experimental geometry, photoelectron spectra, and NMR data supports the importance of optimized geometries for these molecular systems and provides the basis for interpretation of chemical and biological properties. Oxidized forms are shown to be most stable in the planar configuration but also highly flexible about the N(5) - N(10) axis; only 1 kcal/mol is required for a 10° bend. N(10) is generally out of the plane slightly; also, C(9)-methyl substitution introduces nonplanarity. The unsubstituted isoalloxazine is computed to be 0.76 kcal/mol (ΔH) less stable than its isomer, alloxazine. Calculations were also performed on enol as well as quinone-methide tautomeric forms.Reduced flavin geometry depends on methyl substitution pattern: N(10) substituted forms are bent with typical fold angles around 155°, whereas the unsubstituted reduced form is planar. Both oxidized and reduced forms are also flexible.Proton affinities were calculated for protonation and deprotonation of oxidized and reduced forms. Protonation of oxidized forms is favored at N(1) by 10-12 kcal/mol and produces somewhat nonplanar isoalloxazinium ions. In addition, ΔH for the two-electron reduction of lumiflavin is estimated to be -19.7 kcal/mol.In this paper investigations of geometric aspects are presented along with introductory and background material. Orbital structure and electron distribution studies are presented in paper II.
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  • 49
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on MINDO/3 optimized geometries, molecular properties have been computed for lumiflavin and related methylated isoalloxazines. Excellent agreement with UV PES is obtained. Salient differences from previous work are identified in the interpretation of the spectra.Computed partial atomic charges are presented and discussed for both oxidized and reduced forms, including cationic and anionic species. The most polar portion of the isoalloxazine system is pyrimidine-like ring C because of the high polarity of the carbonyl groups. Otherwise, N(1) and N(3) are the most negative ring atoms in the oxidized and reduced forms forms; C(4a) is also very negative in reduced forms. N(5) and N(10) are more negative in reduced than in oxidized forms. It is shown in two-electron reduction that bond length changes are quite localized to the diazadiene portion of the molecule, but that changes in partial charges extend to rings A and B. Only the O=C—NH—C=O moiety does not experience much change in charge.Good correlation is obtained between MINDO/3 partial charges and proton NMR for both the aromatic and methyl protons on ring A, supporting the assignments by Grande and Müller. Also changes in 13C NMR spectra upon reduction are paralleled by changes in computed partial charges. The nature of two-electron reduction is analyzed in terms of changes in HOMO/LUMO as well as geometry and charge distribution. A table of computed properties is included for all compounds studied: total energy, ΔHƒ, ionization potential, electron affinity, and dipole moment.
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  • 50
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    International Journal of Quantum Chemistry 31 (1987), S. 251-268 
    ISSN: 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: 3 Ill.
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  • 51
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    International Journal of Quantum Chemistry 32 (1987), S. 153-162 
    ISSN: 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 molecular conformations of four three-phenyl oligomers of polyaniline are determined via a CNDO/S3 molecular orbital analysis of optical absorption and valenceelectron photoemission spectra for fully hydrogenated (“Leucoemeraldine”: N-4-aminophenyl-N′-phenyl-1, 4 diaminobenzene and N-phenyl-N′-phenyl-1, 4 diaminobenzene), partially hydrogenated (“emeraldine”: N-4-aminophenyl-N′-phenyl- 1, 4-diiminobenzene), and fully oxidized (“pernigraniline”: N-phenyl-N′-phenyl- 1, 4-diiminobenzene) species. The results provide a quantitative description of the optical absorption and photoemission data.
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  • 52
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    International Journal of Quantum Chemistry 32 (1987), S. 163-170 
    ISSN: 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 aromatic (A) and quinoid (Q) forms of polythiophene (PT) have entirely different energy gaps: ∼0.5 eV for the quinoid form and ∼2 eV for the aromatic form, respectively. The energy gaps and stability of derivatives of PT are studied by total MNDO geometry optimization using energy band theory for the total energy calculations followed by a Hückel energy band calculations to approximate the energy band structure. Addition of fused rings to PT reverses the order of stability of the aromatic and quinoid isomers and the ordering in the size of the energy gaps. Small energy gap polymers are suggested on the basis of the calculations.
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  • 53
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    International Journal of Quantum Chemistry 32 (1987), S. 191-198 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical reactions and conformational changes of N-atom systems can be described as displacements in a (3N-6)-dimensional metric configuration space M provided with a global metric. Although space M has a metric, it is not in general a vector space; it is a topological space. In contrast to the commonly used internal configuration spaces based on bond length/bond angle internal coordinates, and having no global metrics, within space M each internal configuration of the nuclei of the molecule corresponds to one and only one point of the space. This property of M is advantageous when analyzing chemical reactions. The global metric of M ensures that differences between any two internal configurations can be interpreted as a distance in this space that allows one to provide M with coordinate systems by turning M into a manifold with boundary. Certain formal reaction paths show some counterintuitive behavior within this space: they may undergo a formal reflection at some points of M. A condition, the tangent criterion, is used for the diagnosis of such reaction paths and for the determination of special nuclear configurations where such reflections occur.
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  • 54
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    International Journal of Quantum Chemistry 32 (1987), S. 245-249 
    ISSN: 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 survey of recent developments in the theory and experimental knowledge of charged interfaces is discussed in relation to the problem of electron transfer reactions. An attempt is made to reformulate the role of the solvent in bulk phase and at surfaces. Furthermore we discuss the effect of position-dependent tunneling on the reaction rate constant assuming simple distribution of the ions near the metallic interface.
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  • 55
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    International Journal of Quantum Chemistry 32 (1987), S. 283-295 
    ISSN: 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 examine the photoaddition of hydroxylazoaromatic compounds and related thione analogs with olefins. By examining the properties of the lowest lying singlet and triplet states, we conclude that the product distribution is best described by the unpaired spin density of the triplet state. This suggests that absorption of light by the aromatic is followed by conversion into the triplet, and this triplet is the active precursor. Since unrestricted molecular orbital calculations are easily performed on the lowest triplet of these aromatics, prediction of possible products is straightforward.
    Additional Material: 7 Ill.
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  • 56
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    International Journal of Quantum Chemistry 32 (1987), S. 355-362 
    ISSN: 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 self-consistent model capable of describing the interaction of a metal electrode/liquid electrolyte interface is presented. As in a real system, a capacity maximum shifted towards positive charges is obtained from the model. The metal is represented by the planar uniform background model (jellium). The solvent is described by a polar liquid whose response to charge is accounted for in terms of the local approximation. The interaction between the metal and ions is modelled by a charged plane placed near the metal surface. Charge neutrality of the whole system is preserved. The present model is a good approximation for highly concentrated solutions.
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  • 57
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    International Journal of Quantum Chemistry 32 (1987), S. 407-415 
    ISSN: 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: Our procedure for employing analytical gradients of ab initio potential energy hypersurfaces in the description of centrifugally distorted molecules is applied to an asymmetric top, namely water. Both single determinantal (HF/6-31G**) and configuration-interaction (CISD/6-31G**) surfaces were utilized. Quartic centrifugal spectroscopic coefficients are obtained in both cases and are in reasonable agreement with experiment. It is shown that the calculated dependence of the energy upon the rotational angular momentum is better represented by a Padé approximant than by the conventional power series.
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  • 58
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    International Journal of Quantum Chemistry 32 (1987), S. 417-423 
    ISSN: 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 discuss the solution of the integral Dirac-Fock equation in momentum space. “Balanced” momentum-space gaussian functions are used to expand the large and small components of the Dirac 4-spinors. We show that this approach, which has been successfully used in atomic Dirac-Fock calculations, works equally well in molecular Dirac-Fock calculations.
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  • 59
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    International Journal of Quantum Chemistry 32 (1987), S. 435-456 
    ISSN: 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 discuss the properties of a phase space distribution function that can be expressed as a Gaussian convolution of the Wigner function corresponding to the oneelectron charge density matrix for a many-electron system. This distribution function is known as the Husimi function. It is real and nowhere negative and can be interpreted as a probability density for finding an electron in a particular coherent state or, equivalently, for finding it in a region of phase space consistent with the uncertainty principle. Information is not lost in the transformation from the Wigner function, which can be recovered. We discuss the relationships among various functions and their Fourier transforms. The Husimi function does not have the ordinary densities as marginals but rather Gaussian convolutions of them, from which the ordinary densities can be recovered. Advantages of the Husimi function over the Wigner function for the interpretation of electronic structure are discussed. Illustrative results for the hydrogen atom and for the nitrogen atom at the SCF level are presented.
    Additional Material: 6 Ill.
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  • 60
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    International Journal of Quantum Chemistry 32 (1987), S. 487-493 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analytical derivatives are dependent upon derivatives of the Ao basis set and the MO relaxation. By separating these effects on derivatives, they can be individually studied. We show that the coupled-cluster single and double (CCSD) model introduces most of the MO relaxation effects required by gradients, hessians, dipole, and polarizability derivatives. This finding should make it possible to simplify analytical derivative evaluation at the CCSD level.
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  • 61
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    International Journal of Quantum Chemistry 32 (1987), S. 513-521 
    ISSN: 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 symmetric group approach is presented for performing large scale, direct configuration interaction (CI) studies of electronic correlation effects in molecules. Two alternative graphical methods are described for representing very large sets of lexically ordered orbital configurations. One is suited for truncations in the number of core orbitals and the other for changes in the number of virtual orbitals. The Hamiltonian matrix elements are constructed using a graphical approach for localizing the one-and two-electron contributions. Compact and direct algorithms are given for calculating the irreducible representation matrices of S(N) for the “line-up” permutations. The program implementation of the CI procedure, PEDICI, calculates directly firstorder molecular one-electron properties and transition probabilities from a multireference space for general excitation schemes.
    Additional Material: 4 Ill.
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  • 62
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    International Journal of Quantum Chemistry 32 (1987), S. 539-545 
    ISSN: 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: Effective core potentials are utilized in conjunction with polarization propagator calculations of excited state properties. The propagator method employed is based on an antisymmetrized geminal power wave function as the reference state. Calculations are presented on the low-lying excited states of HF and NaH. All-electron and valence-electron results are compared for HF. The choice of basis set is found to be very important for obtaining good results.
    Additional Material: 6 Ill.
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  • 63
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    International Journal of Quantum Chemistry 32 (1987), S. 569-572 
    ISSN: 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 nonadiabatic energy correction term of the hydrogen molecule at large separation is discussed to determine whether or not the nuclear motion induces the inter-atomic interaction potential. Nonadiabatic vibrational motion of nuclei induces the internal charge polarization of atoms to give the novel correction term to the London R-6 force. The correction term is (4/M) (1/R3), which is important at large R despite the overwhelming magnitude of nuclear mass.
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  • 64
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    International Journal of Quantum Chemistry 32 (1987), S. 603-612 
    ISSN: 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: 5 Ill.
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  • 65
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    International Journal of Quantum Chemistry 32 (1987), S. 661-668 
    ISSN: 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 MO calculations were carried out for fluoro(porphinato)iron(III) in order to elucidate the origin of the out-of-plane displacement of the iron atom and to analyze vibrational modes of the axial ligand bond. Potential curves as functions of the Fe out-of-plane displacement and Fe—F bond distance were calculated for the ground state. By using these potential curves, the equilibrium iron displacement, Fe—F bond distance, and normal mode frequency of the Fe—F stretching vibration were evaluated. The values are in good agreement with experimental values within the differences 0.02 Å, 0.06 Å, and 50 cm-1, respectively. It has been confirmed that the Fe out-of-plane displacement is caused mainly by the Coulomb repulsion between porphine nitrogens and fluorine anion.
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  • 66
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    International Journal of Quantum Chemistry 32 (1987), S. 677-692 
    ISSN: 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, formulas for two-electron integrals over Cartesian Gaussian functions occurring in the Hylleraas-CI method have been given. This paper reports on the extension of those formula to three- and four-electron integrals and presents test results obtained by using the two-electron integrals for H2 With only 2 p-type polarization functions on each atom, the ground state energy calculated for H2 is only about 20 cm-1 higher than the exact value.
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  • 67
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    International Journal of Quantum Chemistry 32 (1987), S. 713-728 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There is presented a novel, coherent procedure, based on the unitary group, for the computation of the spectra of atoms, molecules, solids, nuclei, and elementary particles. These spectra cover a truly remarkable energy range from a fraction to billions of electron volts. The procedure employs freeon orbitals that are free of energetically inert orbitals; e.g., ordinary spin orbitals for electrons, isospin orbitals for nuclei, and the product of ordinary spin orbitals and color orbitals for baryons. The Pauli principle requires the freeon spaces to be conjugate to the inert spaces. The spaces are spanned by Gel'fand states that have a simple, compact, pictorial representation in the form of Gel'fand structures (tableaux). The Hamiltonian for all systems is a second degree polynomial in the generators of the unitary group with parameters that determine the spectral scale and distribution and whose matrix elements are computed Lie algebraically. The unitary group supplies the unitary group quantum number and is the head group of chains of groups that supply additional quantum numbers.
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  • 68
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    International Journal of Quantum Chemistry 32 (1987), S. 751-751 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 69
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    International Journal of Quantum Chemistry 32 (1987), S. 133-147 
    ISSN: 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 the course of conformational motions of molecules the changes in shapes of electronic charge distributions follow that of the nuclear framework. However, this coupling between the changes in the nuclear geometry and electron density may depend on the actual nuclear displacement; the coupling may be weak or strong for a given conformational motion. It is of some interest to analyze how faithfully the charge density variations follow the nuclear displacements in a family of conformational rearrangements. In certain cases small conformational changes may induce large changes in the shape of charge density distributions, while in other cases large and qualitatively important conformational changes may involve qualitatively inessential distortions in the shape of electron distributions. In this article we describe a new classification of conformations based on those domains of nuclear configuration space within which the „shape groups“ (symmetry independent homology groups) of the electric charge density remain invariant. Such an analysis might be valuable when seeking correlations between molecular structure and certain biological or biochemical activities.
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  • 70
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    International Journal of Quantum Chemistry 32 (1987), S. 341-345 
    ISSN: 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.
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  • 71
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    International Journal of Quantum Chemistry 32 (1987), S. 1-1 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 72
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    International Journal of Quantum Chemistry 32 (1987), S. 171-180 
    ISSN: 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 derivation and formulation of density functional theory, which eliminates the formal and practical inconsistencies and limitations of previous theories and allows its extension to stationary states other than the ground state, is given. The theory presented here can also be stated as a series of three theorems that define a family of its mathematical forms, as far as the physical content of the third theorem can either be implicitly incorporated in the density functional or explicitly in the procedure to find a solution to the equations. Examples of both cases are discussed, including the statement of configuration interaction procedure in density functional form.
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  • 73
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    International Journal of Quantum Chemistry 32 (1987), S. 377-387 
    ISSN: 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 describe a procedure to calculate resonance energies that is based on the addition of a complex perturbation to a one-channel or multichannel description of a quantum system. The perturbation has the effect of modifying the boundary conditions so that the perturbed problem leads to the search of the eigenvalues of a bound system. The energies cannot be exploited directly. A point Padé procedure is subsequently applied to remove the perturbation. Tests are made on a well-known one-channel example. Another application is made to two simple photofragmentation processes: photoionization of the ground state hydrogen atom and photodissociation of the HBr molecule. The complex perturbation in this instance is the change of the photon frequency into a complex quantity.
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  • 74
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    International Journal of Quantum Chemistry 32 (1987), S. 547-554 
    ISSN: 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 the original formulation of the MNDO method, the approximation of two-center two-electron integrals over p orbitals is not rotationally invariant, and the coulombtype integrals do not match their one-center counterparts. In recent computer codes the rotational invariance has been restored by dropping the original approximation for two-center exchange integrals over π orbitals, which at the same time disconnected these too from the one-center values. It is shown in this paper that the rotational invariance problem can be overcome in the framework of the original approximation. It is also demonstrated that the mismatch between the one- and two-center two-electron integrals may be the reason for the too short Si-Si bond lengths predicted by MNDO.
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  • 75
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    International Journal of Quantum Chemistry 32 (1987), S. 563-567 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently developed connected moment expansions (CMXS) for the ground state energy are tested on an exactly soluble N-body problem. For a weak correlation limit the second order CMXS reproduce the correlation energy exactly, whereas for a strong correlation limit they account for half of the correlation energy. Going to higher orders, the CMX-LT approximation appears to be the most effective one. The results indicate that the CMX technique should be promising for the calculation of the correlation energy of other systems.
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  • 76
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    International Journal of Quantum Chemistry 32 (1987), S. 595-602 
    ISSN: 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: Properties of the ground state (X 1Σ) of the BCl molecule are calculated in complete fourth-order many-body perturbation theory. The equilibrium bond distance is determined to be Re = 1.740 Å (Re(exp.) = 1.716 Å). Spectroscopic constants are evaluated from the potential curve and agree well with available experimental data. Static electric properties are computed by the finite-external-electric-field perturbation method. Apparently, no experimental information on these properties is available. Fully numerical Hartree-Fock results are used to estimate basis-set effects on the calculated quantities.
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  • 77
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    International Journal of Quantum Chemistry 32 (1987), S. 623-643 
    ISSN: 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 the propagation step of the cationic polymerization, oxetane reacts with the protonated oxetane formed in the initiation step, with concomitant ring opening of the protonated oxetane. To describe properly bond making or bond breaking, it is necessary to use MC-SCF or CI calculations. We have carried out ab initio MODPOT/VRDDO MRD-CI calculations (by the multireference double excitation-configuration interaction technique of Buenker and Peyerimhoff into which we have also meshed a number of desirable computational options for ab initio calculations on large molecules). The CI calculations were carried out on strictly orthogonalized localized occupied and virtual orbitals in the reaction region, with the remainder of the occupied molecular orbitals being folded into an effective CI Hamiltonian. The calculated potential energy surfaces indicate that a preferred pathway for this reaction resembles an SN2 reaction with the oxygen of the oxetane attacking linearly along the C4—O direction of the protonated oxetane and inversion of the hydrogens around the C4 atom.
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  • 78
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    International Journal of Quantum Chemistry 32 (1987), S. 669-676 
    ISSN: 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: While calculating zero-field splitting terms for the lowest triplet state of 4H-pyran4-thione, at the experimental geometry, it was found that the ground state was unstable with respect to an unrestricted Hartree-Fock perturbation. The smallest fragment of the molecule retaining this instability was found to be diatomic CS. The instability is dependent on the basis set used for the calculation. The instability and its relationship to basis set, equilibrium geometry, and the importance of polarization functions for second row elements has been explored for CS and H2CS as a function of internuclear distance. Minimal basis set calculations involving second row elements may be particularly prone to such instabilities.
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  • 79
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    International Journal of Quantum Chemistry 31 (1987), S. 685-692 
    ISSN: 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 easy method of approximating the electron density of a molecule by expressing it as a sum of squares of atomic orbitals is described. The coefficients are determined by minimizing the error in the electric field. The optimal population analysis is an integration of this optimized density over the orbitals belonging to one atom. The Mulliken population analysis can be interpreted as the integral of a Mulliken density that is a similar expression with fixed coefficients. The two densities are compared in détail using calculations on the water molecule and, more briefly, HF, LiH, BH, and C2H4. The error in the densities is identified and examined. The optimal population analysis is strongly recommended as a practical improvement to the Mulliken populations.
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  • 80
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By expanding the wave function of a system of N particles in terms of products of functions of one and (N-1) particles, the one-particle, nonlocal operator F̂EKT (extended Koopmans' theorem) is determined. It is shown that although this operator is nonhermitian, its eigenvalues and eigenfunctions represent the ionization energies and occupied orbitals, respectively. The eigenfunctions of F̂EKT are the one-particle functions that enter into the expansion of the wave function of the system as partners of the (N-1)-particle wave functions. The eingenvalues are also one-particle energies that, multipled by the orbital occupancy probalities, enter the expression for the total N-particle energy of the system.
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  • 81
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    International Journal of Quantum Chemistry 32 (1987), S. 105-122 
    ISSN: 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 fermion unitary group formulation (UGF) of many-body theory is based on the unitary group U(2n) where n is the number of freeon orbitals. This formulation, which conserves particle-number but not spin, is isomorphic to the particle-number-conserving, second-quantized formulation (SQF). In UGF we derive the familiar diagrammatic algorithm for matrix elements, M(Y) = (-1)H+L where H and L denote the numbers of hole lines and loops in the diagram D(Y) of M(Y). The unitary group derivation is considerably simpler than is the conventional, second-quantized derivation that employs time-dependence, Wick's theorem, normal-order, and contractions. In neither fermion UGF nor SQF is spin conserved. We carry out in UGF the spin-projection (symmetry adaptation to SU(2)) of the fermion vectors and obtain with a spin-free Hamiltonian the same matrix elements as with the freeon UGF (part 24 of this series). The fermion unitary group formulation for a spin-free Hamiltonian should be regarded as an alternate path to spin-free quantum chemistry.
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  • 82
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    International Journal of Quantum Chemistry 32 (1987), S. 123-131 
    ISSN: 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: Various isomers of CH3(H2O)n+ (where n = 1-3) have been studied using self-consistent field gradient techniques. The calculations have largely employed a split valence (4-21G) basis set, although the effects of polarization functions and electron correlation have been considered for a model system. A mechanism for the formation of CH3OH from CH3(H2O)n+, involving linear hydration chains, is proposed, and the relevance of the results to the various proposed pathways for the decomposition of nitrosamine metabolites is discussed.
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  • 83
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    International Journal of Quantum Chemistry 32 (1987) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 84
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    International Journal of Quantum Chemistry 32 (1987), S. 133-147 
    ISSN: 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 symmetry adaptation procedure of Chen et al. [Sciencia Sinica 23, 1116 (1980)], which can account for the invariance properties of the Hamiltonian with respect to any finite point group G, is both modified and adapted to the Clifford algebra unitary group approach (CAUGA). From orthogonal symmetry adapted Mo's, one first constructs a pure configuration many-electron basis adapted to the chain U(ni) ⊃ G ⊃ G(s) in terms of the U(ni) Gel'fand-Tsetlin (GT) basis, where ni is the dimension of the irrep defining a given pure configuration, and G(s) designates the canonical chain supplying a unique labeling. The pure configuration basis is then coupled to the desired G-adapted states using the point group Clebsch-Gordan coefficients and the U(n1) ⊂ U(n1 + n2) ⊂ … ⊂ U(n) basis by using the permutation group outer-product reduction coefficients. This basis can be expressed in terms of the U(n) GT basis by using the U(n) subduction coefficients (SAC'S). The SDC'S are particularly simple for the highest weight states (Hess's) of various subproblems, which can be in turn represented through the U(2n) two-box Weyl tableaux of CAUGA. The non-HWS's are obtained by applying the U(ni) lowering generators to the HWS's. In this way we can directly obtain the spin and point group adapted CAUGA basis. The procedure is illustrated on a nontrivial example.
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    International Journal of Quantum Chemistry 32 (1987), S. 149-164 
    ISSN: 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 Hartree-Fock (HF) equations for the (He)2 system are solved using a suitable exchange perturbation technique. The HF interaction energy is then obtained directly from a rapidly convergent iteration procedure. The method remains convergent for short interatomic distances, where the interaction energy surpasses the energy of intraatomic excitations. The fast convergence of the method is a result of the proper treatment of the exchange-deformation effects. In the region of the van der Waals minimum, these effects account for 50% of the HF deformation energy.
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  • 86
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    International Journal of Quantum Chemistry 32 (1987), S. 165-179 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular path codes are computed for 17 hydrocarbons, including benzenoid alternant, nonbenzenoid alternant, fully aromatic nonalternant, antiaromatic nonalternant, and monoradical hydrocarbons. Comparability conditions of Randić and Wilkins [9-18] based on the theorems of Muirhead and Karamata are imposed on the partial sums of the codes. The distance/similarity matrix is constructed using the individual paths as projections in Euclidean space. Both resonance energies and total pi energies correlate with partial ordering predicted from both comparability and similarity schemes. The normalized codes succeed in discriminating combinatorial properties of the various topologies studied such as conjugated circuits.
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  • 87
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    International Journal of Quantum Chemistry 32 (1987), S. 181-191 
    ISSN: 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 that an easier procedure to the study of molecular electrostatic potentials than the prevalent monopole isopotential approach is to use a dipole as the mapping device: allow the dipole to move on a geometrical surface enclosing the molecule such that the distance between the surface and the nearest atoms of the molecule (closest distance of approach) is fixed, say at 2 Å, calculate the electrostatic interaction energy between the molecule and the dipole at different points of the surface, and let the dipole orient itself along the minimum energy direction and treat these minimum energies as the desired electrostatic potentials. Thus the favorable binding sites of a given molecule for other species along with their relative orientations can be obtained. This procedure has been applied to the nucleic acid bases using the necessary input data from two independent sources. Thus success of the procedure in predicting important features of molecular electrostatic potentials has been demonstrated.
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  • 88
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    International Journal of Quantum Chemistry 32 (1987), S. 193-205 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently developed crystalline cluster method within the framework of the Johnson multiple scattering technique was successfully used in calculations of ionic cubic crystals and the defects with a cubic symmetry. In this paper a simple way of extension of the method to noncubic systems by a partial elimination of “muffin-tin” approximation (MTA) is proposed.The procedure suggested does reduce the intermediate integrals to the one-dimensional ones, and they are calculated analytically. It is supposed that an approach of taking into account the nonspherical shape of the potential inside the “muffin-tin” (MT) spheres will be effective in crystals with an ionic type of chemical bond.
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  • 89
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed analysis of the ΔE(R) curves for nine hydrogen bonded dimers involving HF, H2O, and NH3 as partners, computed with five basis sets (STO-3G, MINI-1, 3-21G, 4-31G, and 6-31G**) and subjected to counterpoise (CP) corrections with three different methods is reported. Using several criteria and tests, the positive effect of full CP corrections for the description obtained with all the basis sets (with the exception of the STO-3G one) is pointed out. The CP correction at the 6-31G** levels is still sizable and improves the results with respect to the estimated Hartree-Fock limits of ΔE(Req) and Req. The results obtained with the application of the full CP correction to the MINI-I energies are of relatively good quality. The STO-3G energies at the SCF level are, on the contrary, overcorrected by the full CP correction and slightly improved by “limited” CP corrections: this basis set, however, is not recommended for calculations of geometries and stabilization energies of H-bonded dimers of this size.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 90
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 249-264 
    ISSN: 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 algorithm to derive symmetry orbitals for one-electron band-structure calculations of one-dimensional crystals presented by Božović and Delhalle [1] has been applied to extend the explicit formulation of symmetry-adapted linear combinations of Bloch sums to any line group isogonal to Cn or Cnv. We also point out how the transformation matrices that block-diagonalize the one-electron eigenvalue equation H(k)C(k) = S(k)C(k)E(k) can be determined. Finally, the extended-Hückel block-matrix dimensions of some typical quasi-one-dimensional transition metal compounds have been tabulated in order to give a measure for computational savings achievable by this technique.
    Additional Material: 2 Tab.
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  • 91
    ISSN: 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 systematic examination of the components of the interaction energy, obtained with the Kitaura and Morokuma method, for nine H-bonded dimers without and with counterpoise corrections (CP) is presented. The nine dimers Hn A … HBHm correspond to all the possible combinations of HF, H2O, and NH3 as electron donors and electron acceptors. The interaction energy and the corresponding components have been computed over a sizable interval of intermolecular distances with five basis sets (STO-3G, MINI-1, 3-21G, 4-31G, 6-31G**) selected among those most extensively used to study interactions in larger systems. The CP corrections to the ΔE components have been obtained with a method, implemented in our group, which permits assignment to the pertinent components of ΔE of a physically reasonable portion of the CP correction even though different CP corrections are adopted. We examine here three versions of the CP correction, namely, the full CP correction (i.e., the original version of Boys and Bernardi) and CP corrections limited to the virtual space of the partner or to the electron donor only. The resulting data are employed to assess the basis set dependence of several models of hydrogen bonding (the electrostatic model, the semiclassical model, etc.) both with and without CP corrections.
    Additional Material: 9 Ill.
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  • 92
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 265-277 
    ISSN: 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 semiempirical MO method SINDO1 is extended to second-row atoms from sodium to chlorine. The basis set has a provision to include d orbitals. To retain rotational invariance in a d orbital set, a number of hybrid integrals has to be included that invalidate the zero differential overlap (ZDO) assumption even in a symmetrically orthogonalized basis set. The inclusion of d orbitals rendered the set-up of integral calculation of the original INDO method impractical. Instead of one subroutine for each integral, all explicitly calculated integrals (overlap, core, electronic repulsion) are now contained in a single subroutine under unifying aspects. The parametrization scheme includes pseudopotentials and adjusts the total energy under inclusion of zero point energies to experimental heats of formation of ground states. The vibrational frequencies for the calculation of zero point energies are obtained from calculated force constants and G matrix elements by a scaling procedure. The results for geometries, energies, and dipole moments are compared with MNDO data.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 93
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 94
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 279-293 
    ISSN: 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: Electrostatic, exchange, classical induction, and charge-transfer components of the He2 interaction energy have been analyzed within our previously proposed SCF interaction energy decomposition scheme [36] employing full counterpoise correction of the basis set superposition error (BSSE). The results have been supplemented by dispersion energies evaluated within the variation-perturbation approach. The basis sets used here have been systematically increased in order to investigate basis set extension effects and perform a thorough test of our decomposition scheme. The results obtained for He2 at its van der Waals minimum (R = 5.6 a.u.) indicate that interaction energy components corrected by the full counterpoise method display reduced basis set dependency, do not seem to be overcorrected by the Jansen-Ros-Boys-Bernardi approach, and converge toward the most accurate values available in the literature. The correct representation of occupied orbitals in He requires the use of at least 1s primitive is Gaussian orbitals. This explains the inconclusive character of previous attempts to resolve the BSSE overcorrection problem within smaller expansions.
    Additional Material: 1 Ill.
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  • 95
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 295-312 
    ISSN: 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 accurate analytical electron density for the beryllium atom is obtained by using a fast and systematic method recently developed and tested for the neon atom. Asymptotic conditions both at the nucleus and at large distances are obeyed. A point-by-point comparison between our density and the one obtained from an almost “exact” configuration interaction wave function shows that differences are less than 0.5% for r between 0 and 5 bohrs and less than 1 % up to 9 bohrs. The accuracy of the density is also assessed by comparing results of density moments and x-ray scattering factors.
    Additional Material: 2 Ill.
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  • 96
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 397-397 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 97
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 399-399 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 98
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 403-403 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 401-401 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 405-406 
    ISSN: 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: 3 Ill.
    Type of Medium: Electronic Resource
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