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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio all-electron and effective core potential calculations on CuCl2-4 (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 245-255 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural and energetic results are reported from a series of ab initio calculations on ground state CuCl2-4 in D2d and D4h conformations. All-electron Hartree-Fock calculations including geometry optimization have been carried out with large basis sets reaching triple-zeta valence plus f-function quality. Several ab initio effective core potentials and valence basis sets for Cu and Cl have been tested and evaluated based on comparisons of calculated results obtained at the Hartree-Fock or correlated (Moller-Plesset perturbation theory) levels with the all-electron and experimental data. The optimized structural parameters provided by all-electron or effective core potential methods are very similar, but they differ from averaged experimental data. Thus, the calculated CuCl bond lengths are typically 0.15-0.20 Å too large, and the ClCuCl bond angle (D2d) is 10-15° too small. The square planar (D4h) conformation represents a transition state and not a structural minimum for CuCl2-4. The energy difference between the two conformations (D4h - D2d) is consistently 16-18 kcal/mol at the Hartree-Fock level but approaches 10-12 kcal/mol at the highest levels of theory applied (UMP4(SDTQ)).
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340829
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  • 2
    Electronic Resource
    Electronic Resource
    The nonplanarity of n-doped polyenes and of carbanions with alkali metal counterions (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 51-57 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using ab initio RHF-SCF-MO theory with the 3-21G basis set and geometry optimization with a gradient method, trans pentadienyl lithium and sodium have been shown to have a carbon backbone in which the middle carbon atom falls ca. 40° out of the plane of the other carbon atoms. The free anion was found to be planar. Optimization of the dilithium octateraene complex (C8H10Li2) with C2 symmetry gave a structure where the hydrocarbon backbone is distorted out of plane and folded about the lithium atoms. A partially optimized C8H10Li2 where the C and H atoms are constrained to remain in-plane lies ca. 0.6 eV above the folded structure. The consequences of the distortion are discussed for the applicability to longer polyenes and n-doped polyacetylene. In a vibrational analysis of C5H7Li and C5H7Na and of allyl Li and allyl Na, two very intense bands near 800 cm-1 appear which are not present in the flat, free allyl and pentadienyl anions. The similarity to the broad band at 800 cm-1 which appears in doped polyacetylene is discussed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340810
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  • 3
    Electronic Resource
    Electronic Resource
    Carbodications. I. The structures and energies of C4H42+ isomers (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 2 (1981), S. 356-360 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: At high levels of ab initio theory (6-31G*//4-31G), the most stable C4H42+ isomer is indicated to be the nonplanar cyclobutadiene dication (1a); the planar form, 1b, is indicated to be 7.5 kcal/mol less stable. The second most stable C4H42+ isomer, the methylenecyclopropene dication, is indicated to prefer the perpendicular (2a) over the planar (2b) arrangement by 7 kcal/mol. The “anti van't Hoff” cyclo-(HB)2C=CH2 system (4), isoelectronic with 2, also prefers the perpendicular conformation (4a), and retains the C=C double bond. The linear butatriene dication (3) is the least stable C4H42+ species investigated. The perpendicular (D2d) arrangement (3a), permitting double allyl cationlike conjugation, is preferred over the planar D2h form (3b) by 26 kcal/mol. The heat of formation of the most stable form of C4H42+, 1a, is estimated to be 623-640 kcal/mol. This species should be thermodynamically stable toward dissociation into smaller charged fragments.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540020316
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic states and barriers to internal rotation in silaallenes (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 571-579 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The electronic states and barriers to internal rotation in allene (1a), 1-silaallene (2a), and 2-silaallene (3a) are investigated computationally using ab-initio molecular orbital methods. Planar geometries with two-, three-, and four-π-electron configurations have been considered as possible transition states (1b-3d). Structures have been optimized at the Hartree-Fock level with a small split valence basis set (3-21G) and higher level calculations with basis sets of split valence (6-31G) and split valence plus polarization function (6-31G*) quality include correlation energy estimates from Møller-Plesset second-and third-order perturbation theory. The electronic barrier to internal rotation in allene is estimated near 53 kcal/mol whereas the corresponding barriers in 1-silaallene and 2-silaallene are considerably smaller, ca. 35 and 20 kcal/mol, respectively. The transition states are predicted to possess bent geometries in all three molecules with open-shell singlet, three-π-electron configurations in 1 and 2 (1c, 2c) but a closed-shell singlet, two-π-electron configuration in 3 (3d).
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030416
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  • 5
    Electronic Resource
    Electronic Resource
    Evaluating polarizable potentials on distributed memory parallel computers: Program development and applications (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 1141-1152 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The efficient evaluation of polarizable molecular mechanics potentials on distributed memory parallel computers is discussed. The program executes at 7-10 Mflops/node on a 32-node CM-5 partition and is 19 times faster than comparable code running on a single-processor HP 9000/735. On the parallel computer, matrix inversion becomes a practical alternative to the commonly used iterative method for the calculation of induced dipole moments. The former method is useful in cases such as free-energy perturbation (FEP) simulations, which require highly accurate induced dipole moments. Matrix inversion is performed 110 times faster on the CM-5 than on the HP. We show that the accuracy which is needed for FEP calculations with polarization can be obtained by either matrix inversion or by performing a large number of iteration cycles to satisfy convergence tolerances that are less than 10-6 D. © 1995 by John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540160908
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular electrostatic potentials and partial atomic charges from correlated wave functions: Applications to the electronic ground and excited states of 3-methylindole (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 979-989 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Procedures have been developed to generate molecular electrostatic potentials based on correlated wave function from ab initio or semiempirical electronic structure programs. A new algorithm for point-wise sampling of the potential is described and used to obtain partial atomic charges via a linear, least squares fit between classical and quantum mechanical electrostatic potentials. The proposed sampling algorithm is efficient and promises to introduce less rotational variance in the potential derived partial charges than algorithms applied previously. Electrostatic potentials and fitted atomic charges from ab initio (HF/6-31G* and MP2/6-31G*) and semiempirical (INDO/S; HF, SECI, and SDCI) wave functions are presented for the electronic ground (S0) and excited (1Lb, 1La) states of 3-methylindole. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130808
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