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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular modeling 3 (1997), S. 182-192 
    ISSN: 0948-5023
    Keywords: Keywords: Frequency-dependent polarizabilities ; quasi-one-dimensional systems ; nonlinear optics ; coupled Hartree-Fock method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Calculations of frequency-dependent polarizabilities of quasi-one-dimensional systems are reported using the coupled Hartree-Fock method recently developed for polymers. Computations have been performed for infinite model chains of hydrogen and water molecules, respectively. The frequency dispersions applying different basis sets agree very well with theoretical results in the literature both for the chain and the respective molecule. In addition the dynamic polarizabilities of the conjugated periodic systems polyacetylene, polycarbonitrile and polyaziridine have been investigated.
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2717-2726 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coupled Hartree–Fock (CHF) equations in second order are derived to calculate dynamic polarizabilities and hyperpolarizabilities for infinite periodic chains. The analytical expressions for the second derivatives of the perturbed crystal orbitals with respect to the quasimomentum k are developed. The first and second derivatives are required on behalf of the definition of the perturbation operator describing the effect of the time-dependent electric field on the electronic structure of the polymer. The computer program has been applied to calculate the tensor elements of the second-harmonic generation and the optical rectification for the model chain poly(water) and the conjugated π-electron system poly(carbonitrile), respectively. The CHF-results are compared with uncoupled Hartree–Fock (UCHF) calculations. © 1999 American Institute of Physics.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 10248-10264 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the formalism for the correction of the band structure for correlation effects of polymers in the framework of a localized orbital approximation, using the quasiparticle model. For this purpose we use in an ab initio framework Møller–Plesset perturbation theory in second order, the coupled cluster doubles method, and its linear approximation. The formalism is applied to a water stack and two different forms of a water chain as model systems to test the reliability of the approximations involved. From our previous work we know that, e.g., in polyacetylene difficulties due to the localizability of the canonical crystal orbitals do not arise from the π or π* bands, but from bands of σ symmetry. Thus we concentrate in this work again on polyacetylene as an example of a realistic polymer. We find that the localized orbital approximation is quite useful also in the case of band structure corrections due to correlation effects. However, the coupled cluster calculations, in particular, turn out to be computationally very costly for infinite systems. But it seems to us that localized orbital approximations are at the moment the only way to make coupled cluster calculations on realistic polymers with covalent bonds between the unit cells possible at all. © 1997 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 379-385 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to the central dogma of molecular biology, information flows in the living cell from DNA through RNA to proteins. Therefore most investigations of cancer initiation try to explain these effects by carcinogen binding to, or radiation hits on, DNA which lead to the first steps of the malignant transformations. On the other hand, recent detailed theoretical investigations have shown that proteins are good disordered hopping conductors (their conductivity is in the order of good conducting amorphous glasses). Their conductivity can be substantially influenced by binding of chemicals or by the effects of radiation if they cause conformational changes (as recent calculations have shown). These effects can also destroy bonds or generate new bonds in proteins. If the affected proteins are regulatory proteins, they can be inactivated in both ways. Namely, on the basis of Warburg's experiments, one can postulate that if the hindrance of oxygen metabolism leads to fermentation, and with it to the malignant transformation, this means also the hindrance of electron flow in the Szent-Györgyi-Krebs cycle. In other words the hindrance of electron transport in this cycle most probably has the same effect as the lack of oxygen, which in this way most probably leads again to a malignant transformation. Finally the inactivation of regulatory enzymes can influence also the regulation of the expression of oncogenes. If in this way oncogenes become overactivated (or antioncogenes become inactive), the changes started by the inactivation of regulatory enzymes become hereditary. It seems that if we look at the cell as a complicated self-regulatory system, primary changes both at their DNA or regulatory protein molecules caused by external agents can disturb its self-regulation and transform it in this way into another stationary, possibly precancerous, state.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 379-385, 1997
    Additional Material: 2 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 54 (1995), S. 89-92 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new boundary treatment, a Hartree-Fock (HF) surface potential model, is proposed to deal with the surface effect in the solid-state cluster calculations using the LCAO-MO-SCF ab initio method. The surface potential arises from one or more atoms, which have no basis function and are added to the calculated cluster system. These atoms are placed in such sites so that the HF potential field of the calculated system should possess a point-group symmetry. The surface potential could be found by the corresponding HF potential using a symmetry operator. The fact that a rather symmetric electronic structure of the asymmetric cluster YBa2CuZn2O7 is obtained using the HF surface potential shows that the surface effect in the cluster calculations could be neutralized to a great extent. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 63 (1997), S. 631-635 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: First, several reminiscences are recalled about the author's encounters with such a beautiful person as Professor Jean-Louis Calais. Since Jean-Louis was very much interested - among other things - in the correlation problem of solids, different methods are reviewed for the correlation correction of the energy bands of 1D and 2D periodic systems as well for the levels of 1D nonperiodic chains. The results obtained show a very good agreement with experiment for the fundamental gap and exciton spectra of different polymers, for the mechanical properties of polyethylene, as well for other not-here-described physical properties of different polymeric systems. The coding of these methods for the relativistic case is in progress. © 1997 John Wiley & Sons, Inc.
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