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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical approach to the molecular conformation of nonfused biheterocycles. Bifurans and furylpyrroles (1987)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 91 (1987), S. 545-551 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100287a011
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  • 2
    Electronic Resource
    Electronic Resource
    Ab Initio Determination of the Geometric Structure and Internal Rotation Potential of 2,2'-Bithiophene (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 4955-4963 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100014a014
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: Theoretical study of the low-lying states of trans-1,3-butadiene [J. Chem. Phys. 97, 7499 (1992)] (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7663-7663 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465116
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical study of the low-lying states of trans-1,3-butadiene (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7499-7506 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present extensive ab initio calculations on the low-lying electronic states of trans-1,3-butadiene within the multireference configuration interaction (MRCI) framework by selecting the configurations with a perturbative criterion. The X 1Ag ground state and 1 3Bu, 1 3Ag, 2 1Ag, and 1 1Bu valence excited states have been calculated at a fixed geometry. The results obtained are in good agreement with previous experimental and calculated values, and could help to understand polyene spectroscopy, photochemistry, and photophysics. The advantages of a MRCI method where the most important contributions to the total MRCI wave function, perturbatively selected, are treated variationally, and the remaining terms are evaluated by means of a perturbational approach, are also discussed. Furthermore, a criterion in order to build a correlation-consistent configuration interaction space is stated and, therefore, a reliable approximation to achieve accurate energy differences is obtained. Several monoelectronic molecular-orbital basis functions are tried in order to select the most adequate to describe each state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463521
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  • 5
    Electronic Resource
    Electronic Resource
    Size-consistent single-reference methods for electronic correlation: a unified formulation through intermediate hamiltonian theory (1996)
    Springer
    Theoretical chemistry accounts 95 (1996), S. 215-241 
    Details
    ISSN: 1432-2234
    Keywords: Dressed CI ; Intermediate hamiltonians ; Many body perturbation theory ; Coupled pair approximations ; Coupled cluster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using the intermediate hamiltonian theory as a unique conceptual frame and the technique of CI matrix dressing, a wide series of single-reference methods for the treatment of the ground state correlation are reviewed, compared, and sometimes improved. These methods range from independent excitation approximation (the very next step beyond MP2) to coupled cluster, going through the so-called electron pair approximations and the (SC)2CI formalism. A hierarchy of these methods can be established according to two criteria: 1. The physical effects incorporated in the model space, the choice of which is flexible. 2. The quality of the evaluation of the coefficients of the external space determinants. This evaluation, which remains based on a single reference expansion of the wave function, may simply ensure the size consistency or incorporate the linked contributions from the outer space. These formulations in terms of diagonalizations of dressed CI matrices avoid convergence problems, but their main advantage is their flexibility, since they apply to multi-reference SDCI spaces as well as to SDCI spaces. The use of a common frame allows one to propose consistent combinations of methods of various costs for the treatment of various parts of the correlation energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02335465
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  • 6
    Electronic Resource
    Electronic Resource
    Conformational behaviour of 2,2′-bipyrrole (1986)
    Springer
    Theoretical chemistry accounts 69 (1986), S. 41-49 
    Details
    ISSN: 1432-2234
    Keywords: 2,2′-Bipyrrole ; Rotational barrier ; MO calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rotational potential around the interannular bond in 2,2′-bipyrrole has been calculated making use of standard minimal STO-3G and split valence 4-31G basis sets. Geometrical optimization concerning the most significant interannular internal parameters has been performed with both basis sets. The trans conformer is predicted to be more stable than the cis. The minimal basis set predicts the existence of a cisoid-gauche minimum which after limited optimization becomes very shallow and it seems to be an artifact of the rigid rotor approximation. At 4-31G level, both the trans and cis conformers represent maxima in the potential curve and two gauche minima appear at θ=46.0° and θ=147.6°, the latter being the absolute minimum. The absolute maximum of the potential curve corresponds to the cis conformer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526291
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  • 7
    Electronic Resource
    Electronic Resource
    Size-consistent single-reference methods for electronic correlation: a unified formulation through intermediate hamiltonian theory (1997)
    Springer
    Theoretica chimica acta 95 (1997), S. 215-241 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Dressed CI ; Intermediate hamiltonians ; Many body perturbation theory ; Coupled pair approximations ; Coupled cluster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  Using the intermediate hamiltonian theory as a unique conceptual frame and the technique of CI matrix dressing, a wide series of single-reference methods for the treatment of the ground state correlation are reviewed, compared, and sometimes improved. These methods range from independent excitation approximation (the very next step beyond MP2) to coupled cluster, going through the so-called electron pair approximations and the (SC)2CI formalism. A hierarchy of these methods can be established according to two criteria: 1. The physical effects incorporated in the model space, the choice of which is flexible. 2. The quality of the evaluation of the coefficients of the external space determinants. This evaluation, which remains based on a single reference expansion of the wave function, may simply ensure the size consistency or incorporate the linked contributions from the outer space. These formulations in terms of diagonalizations of dressed CI matrices avoid convergence problems, but their main advantage is their flexibility, since they apply to multi-reference SDCI spaces as well as to SDCI spaces. The use of a common frame allows one to propose consistent combinations of methods of various costs for the treatment of various parts of the correlation energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050193
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  • 8
    Electronic Resource
    Electronic Resource
    A study of coronene - coronene association using atom - atom pair potentials (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 567-573 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the coronene - coronene association using different interaction potentials based on an atom-atom pair potential proposed by Fraga has been performed. The interaction potentials employed differ in the way the electrostatic and/or dispersion contributions are computed. The influence of both contributions on the geometries predicted for the coronene dimer is discussed in order to analyze the effectiveness of the different interaction potentials. The stationary points found in each interaction energy hypersurface are characterized by calculating the Hessian eigenvalues. Results are discussed in the light of those previously reported for the benzene dimer. Stacked-displaced structures are suggested to be the preferred conformations for the coronene - coronene association. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 9
    Electronic Resource
    Electronic Resource
    Are most of the stationary points in a molecular association minima? Application of Fraga's potential to benzene-benzene (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 647-654 
    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 importance of characterizing the stationary points of the intermolecular potential by means of Hessian eigenvalues is illustrated for the calculation of the benzene-benzene interaction using an atom-to-atom pair potential proposed by Fraga (FAAP). Two models, the standard one-center-per atom and another using three-centers-per atom due to Hunter and Sanders, are used to evaluate the electrostatic contributions and the results are compared. It is found in both cases that although using low-gradient thresholds allows optimization procedures to avoid many stationary points that are not true minima computing time considerations makes the usual procedure of using high-gradient thresholds [say, 10-2 kj/(mol Å)] as the most efficient. Moreover, this later procedure can be recommended because the actual minima can be characterized by means of Hessian eigenvalues even if these high-gradient thresholds are used, and further decreasing of the convergence criterion does not imply significant modifications in the geometric parameters of the minima. The possible advantages of using the three-centers-per-atom model for the calculation of molecular associations between delocalized systems are also discussed on the basis of the agreement of the benzene-benzene results with experimental and theoretical data taken from the literature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540140604
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