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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational polarizability of polyacetylene chains (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10796-10807 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the double harmonic oscillator approximation, ab initio vibrational contributions to the static electric dipole polarizability have been computed for the all-trans polyacetylene chains homologous series. Atomic basis set and electron correlation effects have been studied on ethylene and trans-butadiene as well as the use of semiempirical Hamiltonians. By using the 6-31G* atomic basis set within the Hartree–Fock and the second order Møller–Plesset procedures as well as by using semiempirical Austin model 1 Hamiltonians, the evolution with chain length of the vibrational polarizability per structural unit has been investigated and compared to the electronic contribution. Although smaller than the electronic contributions (αvibration≈10% αelectronic), the longitudinal component to the polarizability presents a similar exaltation as chain length grows, but a slower saturation to an asymptotic value per unit cell. Inclusion of electron correlation via the second order Møller–Plesset technique turns out to reduce the longitudinal component calculated at the Hartree–Fock level, but to increase the transversal and perpendicular components. Whereas it reproduces correctly the evolution with chain length of the vibrational polarizability tensor components, the Austin model 1 technique underestimates the longitudinal term and overestimates the perpendicular term. The major contribution to the vibrational polarizability results from large charge fluxes associated with asymmetric stretching motions of the carbon backbone and with the torsion motions presenting very low vibrational frequencies. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467830
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  • 2
    Electronic Resource
    Electronic Resource
    Erratum: "Assessment of conventional density functional schemes for computing the polarizabilities and hyperpolarizabilities of conjugated oligomers: An ab initio investigation of polyacetylene chains" [J. Chem. Phys. 109, 10489 (1998)] (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11664-11664 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479106
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational and electronic second hyperpolarizabilities of all-trans polysilane chains (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4624-4637 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational (γLv) and electronic (γLe) longitudinal second hyperpolarizabilities of increasingly large polysilane chains are determined at the Hartree–Fock 6-31G level by adopting both the double harmonic oscillator approximation and the infinite optical frequency finite field relaxation procedure. The relative importance of the electronic, Raman, infrared/hyperRaman and lowest-order anharmonicity contributions to the second hyperpolarizability is evaluated for the most common nonlinear optical (NLO) processes. At the double harmonic oscillator level of approximation the most contributing vibrational normal modes to γLv are characterized as a function of the polysilane chain length. Comparisons with experimental and other theoretical studies are carried out in what concerns the infrared and Raman vibrational spectra as well as the NLO properties of various oligosilanes and polysilanes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477067
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  • 4
    Electronic Resource
    Electronic Resource
    Assessment of conventional density functional schemes for computing the polarizabilities and hyperpolarizabilities of conjugated oligomers: An ab initio investigation of polyacetylene chains (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 10489-10498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: DFT schemes based on conventional and less conventional exchange-correlation (XC) functionals have been employed to determine the polarizability and second hyperpolarizability of π-conjugated polyacetylene chains. These functionals fail in one or more of several ways: (i) the correlation correction to α is either much too small or in the wrong direction, leading to an overestimate; (ii) γ is significantly overestimated; (iii) the chain length dependence is excessively large, particularly for γ and for the more alternant system; and (iv) the bond length alternation effects on γ are either underestimated or qualitatively incorrect. The poor results with the asymptotically correct van Leeuwen–Baerends XC potential show that the overestimations are not related to the asymptotic behavior of the potential. These failures are described in terms of the separate effects of the exchange and the correlation parts of the XC functionals. They are related to the short-sightedness of the XC potentials which are relatively insensitive to the polarization charge induced by the external electric field at the chain ends. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477731
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  • 5
    Electronic Resource
    Electronic Resource
    Linear and nonlinear polarizabilities of polydiacetylene and polybutatriene chains: An ab initio coupled Hartree–Fock investigation (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2463-2480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio Hartree–Fock 6-31G longitudinal polarizabilities and second hyperpolarizabilities of polydiacetylene and polybutatriene oligomers are computed and, then, extrapolated to the infinite polymer limit. Both the electronic and vibrational components are obtained with the latter evaluated in the double harmonic approximation. For static fields the electronic hyperpolarizability of the butatrienic form is almost 50 times larger than the acetylenic form; the ratio of the vibrational to the electronic component is 0.86 for the latter and 3.3 for the former. Thus, the two components are sensitive to the difference in bond length alternation (BLA) in different ways. Depending upon the particular nonlinear process it is shown that the vibrational hyperpolarizability may remain large even at optical frequencies. Three intense Raman-active k=0 modes dominate the vibrational component. At the level of theory used here these modes occur in the frequency range 1000–2500 cm−1 and they consist of changes in the BLA as well as hydrogen wagging motions. For polydiacetylene, there is a 1:1 relation with the corresponding vibrations that make the most important hyperpolarizability contributions in polyacetylene and polyyne.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474588
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  • 6
    Electronic Resource
    Electronic Resource
    Nonresonant frequency dispersion of the electronic second hyperpolarizability of all-trans polysilane chains: An ab initio TDHF oligomeric approach (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 751-761 
    Details
    ISSN: 0020-7608
    Keywords: electronic second hyperpolarizability ; polysilane ; frequency dispersion ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The frequency-dependent electronic second hyperpolarizability of increasingly large polysilane chains is computed for the most common nonlinear optical (NLO) processes at the time-dependent Hartree-Fock level with the 6-31G atomic basis set. Due to σ-conjugation, the longitudinal component (γLe) turns out to be dominant. Its nonresonant dispersion relations are described by the coefficients of the power expansion formula, γLe(-ωσ; ω1, ω2, ω3)=γLe(0; 0, 0, 0)[1+AωL2+BωL4+CωL6+···], where ωL2=ωσ2+ω12+ω22+ω32 and γLe(0; 0, 0, 0) is the static limit value. In the infinite chain length limit, the CHF/6-31G static longitudinal electronic second hyperpolarizability per Si2H4 unit cell is estimated to attain 463±10×103 a.u. whereas the A coefficient reaches 27.8±0.9 a.u. The accuracy that could be reached from using this power expansion expression for estimating the second hyperpolarizability for other optical frequencies is discussed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 751-761, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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