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  • 1
    Electronic Resource
    Electronic Resource
    Calculation of polymer elastic moduli using semiempirical methods (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 529-540 
    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: Extensional elastic moduli have been calculated for several organic high polymers based on the modified neglect of diatomic overlap (MNDO) Hamiltonian. Standard semiempirical methods, by application of the Born-von Karman boundary conditions, can be used to calculate heats of formation of polymer chain sections, or computational unit cells, called clusters. Unit cell heats of formation at elongated translation vectors, combined with experimental or estimated densities, allow for the calculation of elastic moduli. Two potential sources of error were identified: (a) finite geometry optimization can result in pseudorandom errors in the calculated heat of formation, and (b) anharmonic distortion can become significant at large strains. Errors due to both causes can typically be minimized if strains between 3 and 10% are selected. As expected, the calculated moduli, although higher than those observed experimentally, agree with longitudinal values for perfectly oriented systems.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300746
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  • 2
    Electronic Resource
    Electronic Resource
    Structure and electronic structure of polyacene (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 305-313 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that infinite long polyacene chains may have three energetically close but structurally distinct isomers (a symmetrical, sym, form and two lower symmetry forms: one with double bonds in a trans and another isomer with double bonds in a cis pattern). The energetics is based on solid state MNDO theory. We discuss that the symmetrical form has a substantial energy gap Eg in the Hartree-Fock approach owing to exact exchange terms, which are nonlocal. Broken symmetry Hartree-Fock (HF) solutions for polyacene are also described. An angularly distorted structure suggested earlier on Jahn-Teller grounds is found to be energetically not favorable.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560350207
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  • 3
    Electronic Resource
    Electronic Resource
    Ground states of molecules. 67.For part 66, see ref. 1.MNDO Calculations for compounds containing iodine (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 358-362 
    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: MNDO has been parametrized for iodine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to II. Heats of formation, molecular geometries, ionization energies, and dipole moments are reproduced with useful accuracy.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540050413
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  • 4
    Electronic Resource
    Electronic Resource
    Semiempirical vibrational and electronic structures of C60 and C70 (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1157-1162 
    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 and vibrational structures of C60 and C70 have been calculated at the PM3 semiempirical level. C60 has a partially delocalized structure, while C70 has both a localized set and a delocalized set of MOs. As with AM1 and MNDO, PM3 predicts the heat of formation of C70 to be greater than that of C60, and that C70 is the thermodynamically more stable species. Calculation of the normal modes was accelerated over 40 times by limited use of symmetry theory.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120915
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  • 5
    Electronic Resource
    Electronic Resource
    Optimization of parameters for semiempirical methods II. Applications (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 221-264 
    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: MNDO/AM1-type parameters for twelve elements have been optimized using a newly developed method for optimizing parameters for semiempirical methods. With the new method, MNDO-PM3, the average difference between the predicted heats of formation and experimental values for 657 compounds is 7.8 kcal/mol, and for 106 hypervalent compounds, 13.6 kcal/mol. For MNDO the equivalent differences are 13.9 and 75.8 kcal/mol, while those for AM1, in which MNDO parameters are used for aluminum, phosphorus, and sulfur, are 12.7 and 83.1 kcal/mol, respectively. Average errors for ionization potentials, bond angles, and dipole moments are intermediate between those for MNDO and AM1, while errors in bond lengths are slightly reduced.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100209
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  • 6
    Electronic Resource
    Electronic Resource
    Calculation of the nonlinear optical properties of molecules (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 82-87 
    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: A finite-field method for the calculation of polarizabilities and hyperpolarizabilities is developed based on both an energy expansion and a dipole moment expansion. This procedure is implemented in the MOPAC semiempirical program. Values and components of the dipole moment (μ), polarizability (α), first hyperpolarizability (β), and second hyperpolarizability (γ) are calculated as an extension of the usual MOPAC run. Applications to benzene and substituted benzenes are shown as test cases utilizing both MNDO and AM1 Hamiltonians.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540110110
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  • 7
    Electronic Resource
    Electronic Resource
    Numerical sensitivity of trajectories across conformational energy hypersurfaces from geometry optimized molecular orbital calculations: AM1, MNDO, and MINDO/3 (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 387-398 
    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 monocyclic β-lactam [[4(S)-methyl-2-oxo-1-azetidinyl]thia]acetic acid was studied by the semiempirical molecular orbital methods AM1, MNDO, and MINDO/3. Using the reaction coordinate option in the program MOPAC on VAX and Cray X-MP computers, the potential energy curve was calculated for rotation of the C2-N1-S-C torsional angle in the conformationally flexible side chain while optimizing all other geometrical variables in the molecule. The trajectory taken during geometry optimization was found to be sensitive to the computer, the program version, the convergence criteria, and the degree of code optimization used in the calculation. In order to reduce the likelihood of spurious results, conformational or reaction energy hypersurfaces need to be calculated with the more precise SCF convergence and minimization criteria available in programs for MINDO/3, MNDO, and AM1 calculations. The nitrogen in the model β-lactam antibiotic is predicted to invert periodically as the dihedral angle to the exocyclic N-substituent sweeps through 360°.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090414
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  • 8
    Electronic Resource
    Electronic Resource
    Optimization of parameters for semiempirical methods I. Method (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 209-220 
    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: A new method for obtaining optimized parameters for semiempirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method. The method uses derivatives of calculated values for properties with respect to adjustable parameters to obtain the optimized values of parameters. The large increase in speed is a result of using a simple series expression for calculated values of properties rather than employing full semiempirical calculations. With this optimization procedure, the rate-determining step for parameterizing elements changes from the mechanics of parameterization to the assembling of experimental reference data.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100208
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  • 9
    Electronic Resource
    Electronic Resource
    Optimization of parameters for semiempirical methods. III Extension of PM3 to Be, Mg, Zn, Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Pb, and Bi (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 320-341 
    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: Using a recently developed procedure for optimizing parameters for semiempirical methods,1 PM3 has been extended to a total of 28 elements. Average ΔHf errors for the newly parameterized elements are Be: 8.6, Mg: 8.4, Zn: 5.8, Ga: 14.9, Ge: 11.4, As: 8.5, Se: 11.1, Cd: 2.6, In: 11.3, Sn: 9.0, Sb: 13.7, Te: 11.3, Hg: 6.8, Tl: 6.5, Pb: 7.4, and Bi: 10.9 kcal/mol. For some elements the paucity of data has resulted in a method, which, while highly accurate, is likely to be only poorly predictive.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120306
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  • 10
    Electronic Resource
    Electronic Resource
    Reply to “Comments on a comparison of AM1 with the recently developed PM3 method” (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 543-544 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540110414
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