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  • 1
    Electronic Resource
    Electronic Resource
    Analytical time-dependent Hartree–Fock schemes for the evaluation of the hyper-Raman intensities (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2481-2488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two analytical procedures based on the time-dependent Hartree–Fock (TDHF) scheme are elaborated to evaluate the first derivatives of the dynamic first hyperpolarizability with respect to atomic Cartesian coordinates. In the first scheme, the mixed third-order TDHF equations are solved iteratively to obtain the third derivatives of the linear combination of atomic orbitals coefficients twice with respect to external dynamic electric fields and once with respect to atomic Cartesian coordinates. The second takes advantage of the 2n+1 rule and interchange relations to express the first derivatives of the dynamic first hyperpolarizability with respect to atomic Cartesian coordinates in terms of lower-order derivatives. Both procedures have been implemented in the GAMESS quantum chemistry package. Applications focus on the characterization of the frequency dispersion of the first derivatives of the first hyperpolarizability with respect to vibrational normal coordinates of H2O, NH3, and CH4 as well as on the determination of nonresonant hyper-Raman intensities within the double harmonic oscillator approximation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1490596
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  • 2
    Electronic Resource
    Electronic Resource
    Time-dependent Hartree–Fock schemes for analytical evaluation of the Raman intensities (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6293-6299 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the time-dependent Hartree–Fock method two analytical schemes are elaborated for determining the derivatives of frequency-dependent polarizability with respect to atomic Cartesian coordinates. The first scheme is iterative and consists in determining the mixed derivatives of the density matrix with respect to atomic Cartesian coordinates and dynamic electrical fields. The second takes advantage of the 2n+1 rule to express the polarizability derivatives in terms of first-order derivatives. Both schemes are implemented in the GAMESS program. They enable the fully analytical evaluation of the Raman intensities with inclusion of the frequency dispersion. The potential of these methods is illustrated by determining the polarizability derivatives and Raman intensities of small molecules. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398310
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio investigation of doping-enhanced electronic and vibrational second hyperpolarizability of polyacetylene chains (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 3935-3946 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of charging on the longitudinal second hyperpolarizability of polyacetylene (PA) chains containing up to nearly 70 carbon atoms has been investigated ab initio by characterizing chains with and without an explicit alkali atom (Li, Na, K) as dopant. Whereas charging dramatically enhances the static electronic and vibrational hyperpolarizabilities, γLe(0) and γLv, of an isolated chain at intermediate chain lengths, the presence of an alkali atom counterion substantially reduces this effect. As the size of the alkali atom increases, most properties, including the hyperpolarizabilities, approach those of the isolated chain. Detailed analysis shows that the behavior of γLe(0) is most simply explained in terms of a reduced electrostatic pinning potential due to increased distance between chain and counterion. At all chain lengths studied γLe(0) of PA is enhanced by alkali doping. For chains containing 50 carbon atoms (NC=50), the increase due to K doping is about 9×107 a.u., which more than doubles the value for an undoped chain of similar length. The normalized quantity γLe(0)/NC exhibits a maximum for the isolated soliton (at about NC=61) that is over four times that of the infinite undoped (and unbent) chain. When the alkali dopant is taken into account this maximum diminishes considerably and shifts to larger NC than we have considered. In comparison with the maximum for the undoped species (at NC=∞) there is a small enhancement of γLe(0)/NC for K doping, but none for either Li or Na doping at the coupled-perturbed Hartree–Fock (CPHF)/6-31G level of theory. Intermediate length isolated chains bearing a charged soliton show order of magnitude increases in γv for the degenerate four-wave mixing (DFWM) and, especially, electric field-induced second harmonic generation (dc-SHG) processes compared to undoped PA. As in the case of γLe(0) this enhancement persists, but is significantly reduced when the dopant atom is included. Vibrational anharmonicity, which contributes only to the dc Kerr effect at our level of treatment, is much more important in the doped than undoped species. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1446046
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  • 4
    Electronic Resource
    Electronic Resource
    Comment on "Calculation of ab initio dynamic hyperpolarizabilities of polymers" [J. Chem. Phys. 110, 2717 (1999)] (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1616-1617 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We evaluate the static and dynamic electronic longitudinal polarizability and first hyperpolarizability of infinite poly-water by using the same geometry, the same orientation and the same basis set as Otto et al. but by applying the finite oligomer technique. We show that for the first hyperpolarizability, the polymeric values per unit cell calculated by Otto et al. are inconsistent by several orders of magnitude with respect to the infinite oligomer limit. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480727
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  • 5
    Electronic Resource
    Electronic Resource
    Anharmonicity contributions to the vibrational second hyperpolarizability of conjugated oligomers (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1011-1019 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Restricted Hartree–Fock 6-31G calculations of electrical and mechanical anharmonicity contributions to the longitudinal vibrational second hyperpolarizability have been carried out for eight homologous series of conjugated oligomers—polyacetylene, polyyne, polydiacetylene, polybutatriene, polycumulene, polysilane, polymethineimine, and polypyrrole. To draw conclusions about the limiting infinite polymer behavior, chains containing up to 12 heavy atoms along the conjugated backbone were considered. In general, the vibrational hyperpolarizabilities are substantial in comparison with their static electronic counterparts for the dc-Kerr and degenerate four-wave mixing processes (as well as for static fields) but not for electric field-induced second harmonic generation or third harmonic generation. Anharmonicity terms due to nuclear relaxation are important for the dc-Kerr effect (and for the static hyperpolarizability) in the σ-conjugated polymer, polysilane, as well as the nonplanar π systems polymethineimine and polypyrrole. Restricting polypyrrole to be planar, as it is in the crystal phase, causes these anharmonic terms to become negligible. When the same restriction is applied to polymethineimine the effect is reduced but remains quantitatively significant due to the first-order contribution. We conclude that anharmonicity associated with nuclear relaxation can be ignored, for semiquantitative purposes, in planar π-conjugated polymers. The role of zero-point vibrational averaging remains to be evaluated. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480651
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  • 6
    Electronic Resource
    Electronic Resource
    Study of excited states of polyethylene in the Hartree–Fock, Tamm–Dancoff, and random-phase approximations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6831-6836 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations of the excitonic spectra of all-trans polyethylene in the Hartree–Fock, Tamm–Dancoff, and random-phase approximations. For the formulation of approximations beyond Hartree–Fock level, we have used the particle–hole propagator technique. In the first case the interaction between the excited electron and hole is neglected and in the latter two cases it is taken into account at first order in electron–electron interaction. Using the 3–21G atomic basis set, the elementary gap is reduced from about 17 eV at the Hartree–Fock level to 13 eV in the Tamm–Dancoff approximation. The spectra in both approximations are also different. The difference between the results obtained in the Tamm–Dancoff and the random-phase approximations is very small. We discuss the densities of exciton states for different exciton quasi momenta (K=0 or K=π/a), different band interactions and different spins. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469119
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  • 7
    Electronic Resource
    Electronic Resource
    Long-range effects in optimizing the geometry of stereoregular polymers. II. Hydrogen fluoride chains as a working example (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5324-5330 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use linear hydrogen fluoride chains to evaluate the efficiency of the long-range approach developed in the first paper of this series. A wide panel of tests and comparisons are carried out in order to understand the influence of the parameters on the quality of the forces and the accuracy of the optimized geometry. The long-range corrections are demonstrated to be essential for tight optimizations as well as to fasten the calculation procedure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479791
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  • 8
    Electronic Resource
    Electronic Resource
    Long-range effects in optimizing the geometry of stereoregular polymers. I. Formalism (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5306-5323 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop an original methodology to calculate analytically the long-range (LR) Coulombic effects to be included in Hartree–Fock forces computed on stereoregular polymers. The technique presented, based on multiple Taylor series expansions, is completely general and can be easily extended to all orders of expansion and to geometrical derivatives of higher order. In the McMurchie Davidson or similar schemes, the LR terms are added directly to Hermite integrals and LR effects are naturally considered during the computation of the energy and its derivatives. Each type of derivative (nuclear-repulsion energy, overlap and kinetic energy integrals, electron–nuclear attraction and two-electron integrals) is examined to quantify the impact of LR corrections. It turns out that the lattice sums of the gradients evaluated on a model macromolecule converge much faster when including those corrections. In addition, the dependence of the energy with respect to the unit cell length is for the first time considered in full details. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479790
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  • 9
    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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  • 10
    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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