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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 1707-1708 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 109 (1987), S. 107-113 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 96 (1974), S. 97-103 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 99 (1977), S. 5040-5044 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the phase transition to the conducting state in a system of 2D charge-transfer excitons (CTEs) at a donor-acceptor interface. The phase transition arises due to strong dipole-dipole repulsion between CTEs which stimulates the population of free carriers in higher energy states even at low temperature. We use the computer simulations with the random distribution of excitons, with finite lifetime explicitly taken into account. The critical concentration of CTEs and their energy distribution are calculated. We also discuss the possibility of observing the predicted phenomena.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1067-1076 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Diagrammatic valence-bond (DVB) theory is extended to dynamic nonlinear susceptibilities of interacting π electrons in Pariser–Parr–Pople (PPP) or other quantum cell models whose correlated ground state ||G〉 is known. Corrections φ(1)(ω) and φ(2)(ω2,ω1) to ||G〉 due to oscillating electric fields are found directly as linear combinations of VB diagrams. Any nonlinear optical coefficient is reduced to matrix elements that implicitly include all excited states, as verified for shorter polyenes. Static and dynamic χ(3) coefficients for cis and trans polyenes to N=12 carbons illustrate the importance of retaining the full spectrum. The coefficients βijk(ω,ω) for second harmonic generation are found for polar molecules like aniline and nitroaniline. Divergent responses are treated by lifetimes Γ for the resonant states, as shown for third harmonic generation in hexatriene with Γ=0 and in octatetraene with Γ〉0. Electron–electron interactions reverse the sign of γijkl(ω,ω,ω) in linear polyenes, except for the largest xxxx coefficient along the chain, and strongly decrease their magnitude and size dependence. The DVB procedure is checked against transition moments, noninteracting π electrons in Hückel models, explicit sums over all excited states, and is compared to recent approximate PPP calculations for the nonlinear optical (NLO) coefficients of linear polyenes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5166-5167 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7439-7448 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular exciton methods are extended to obtain excited-state shifts of parallel conjugated strands arising from interchain Coulomb interactions. A method is developed to evaluate second-order corrections involving π-electron dispersion forces, with exact Pariser–Parr–Pople states of isolated segments as zeroth-order functions. Crystal shifts are estimated for polyacetylene (PA) at interchain separation d=3.9 A(ring); the two-photon excitation to the covalent 2 1Ag state is hardly shifted, but the one-photon excitation to 1 1Bu is red shifted by ∼0.30 eV and specific higher n 1Ag states are strongly red shifted by ∼1 eV. Their stabilization correlates with charge separation and ionicity in the excited state. Excitation shifts due to π-electron dispersion forces do not parallel changes in the static polarizability and show unusual long-range behavior of d−3 in the interchain separation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3330-3338 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hopping transport in molecularly doped polymers (MDPs) is usually modeled in terms of energetic disorder corresponding to a Gaussian distribution of states, g(ε,σ), whose width σ is taken from experiment. Time-of-flight profiles indicate normal transport and finite mean dwell time 〈τ(T,E)〉. At zero field, thermal equilibrium and detailed balance are shown to yield 〈τ(T)〉 exactly for hopping rates that are products of energetic and geometrical factors. Hopping in g(ε,σ) for standard rates such as Miller-Abrahams, Marcus, or symmetric leads to ln〈τ(T)〉 that goes strictly as T−2 only for symmetric rates. Disorder-induced steps dominate the zero-field mobility μ(T). Monte Carlo simulations with Marcus rates show that extra steps depend on the overall disorder. Dilution and orientation increase the slope of ln μ(T) vs T−2. We interpret extra steps using an auxiliary lattice with spacing a′ chosen to give the same μ(T). Evidence for disorder-induced steps comes from previous studies with variable donor concentration in the same polymer, from much larger mobility changes than the concentration ratio, and from modeling of tritolylamine:polystyrene systems. Exact dwell times for hopping in g(ε,σ) show that current estimates of σ are upper bounds that neglect geometrical disorder. They provide direct tests for the convergence of simulations, either in terms of 〈τ(T)〉 or the distribution of visited sites in an infinite random walk. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3133-3140 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The diamagnetic susceptibility χ of half-filled fermion models with N=4n+2 sites is related to chemical shifts in molecules and charge stiffness in extended systems. The slow evolution of χ(N) with N in Hubbard models or spinless fermions indicates a small energy gap, as known from exact solutions of regular chains. A gap due to alternating transfer integrals (1±δ) suppresses χ for Nδ〉1, but is a small correction for Nδ〈1. Exact ring currents Nχ of Pariser–Parr–Pople (PPP) and Hubbard models are extended to N=18 in D18h symmetry. Hydrocarbon PPP parameters account for the anisotropy of proton shifts in 14 and 18 annulenes, for smaller shifts at larger N, and for larger shifts of anions with 4n+2 π-electrons. Fermion models with arbitrary spin-independent interactions are shown to have vanishing χ for open boundary conditions (chains) at half filling or finite N. Diamagnetic currents in molecules require rings but are not sensitive to small bond-length variations, while an energy gap rather than topology enters in the charge stiffness of extended systems. Although formally identical, χ has different applications in finite and extended systems and its convergence with N can be rapid or very slow. Spin–charge separation reflects correlations rather than topology in half-filled Hubbard, PPP, and spinless fermion models; 4n and 4n+2 rings with oppositely signed χ show similar spin–charge separation with increasing correlations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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