Theoretical Aspects of Conducting Polymers: Electronic Structure and Defect States

Baeriswyl, D.

doi:10.1007/978-94-009-5299-7_1

Cited by 17 publications

(3 citation statements)

References 125 publications

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“…We further add, that in all three cases presented in Figure 3, the energy differences between 1Bu and 2Ag-excited states exhibit a similar trend (increase with N) as that shown in Figure 4. It is interesting to observe that the quantitative results obtained with the third set of parameters (c) appear to be less than desirable, which may be related to the large deviation of corresponding A from its more accepted value (A 2 0.2) [20].…”

Section: Resultsmentioning

confidence: 97%

The low‐lying excitation energies of polyenes investigated with a chain‐length‐dependent screened potential

Siregar¹,

Tjia²

1993

Int J of Quantum Chemistry

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The chain-length dependencies of 2Ag and 1Bu excitation energies as well as their unexpected inversion observed experimentally in trans-polyenes have so far been explained satisfactorily only in terms of configuration interactions within the standard Pariser-Pan-Pople (PPP) parametrization scheme with at least double excitations involving prohibitively large computational labor for long polyenes. A simpler calculation allowing nonzero differential overlap and employing restricted (first-order) single-excitation configuration interaction with chain-length-dependent screened potential is shown to provide an adequate alternative for the studies of those basic spectroscopic features of polyene excited states. The screening factor is parametrized in accordance with the chain-length-dependent behavior of the electrical polarizabilities of polyenes derived within the standard PPP approximation scheme. 0 1993 John Wiley & Sons, Inc.

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Section: Resultsmentioning

confidence: 97%

The low‐lying excitation energies of polyenes investigated with a chain‐length‐dependent screened potential

Siregar¹,

Tjia²

1993

Int J of Quantum Chemistry

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“…(A6) can also be used to relate two different systems with similar bond orders, such as benzene and graphene. In fact, an essentially linear function is obtained if we plot the average bond orders of different systems versus their average bond lengths [66]. From the slope of these data one can deduce a value α/K ≈ 0.1 Å.…”

Section: Discussion and Outlookmentioning

confidence: 95%

Infrared ellipsometry study of the charge dynamics in K$_3$\,\!p-terphenyl

He,

Marsik,

Mardelé

et al. 2023

Preprint

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We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline Kxpterphenyl samples with nominal x = 3, for which signatures of high-temperature superconductivity were previously reported. The infrared spectra are dominated by two Lorentzian bands with maxima around 4 000 cm −1 and 12 000 cm −1 which, from a comparison with calculations based on a Hückel model are assigned to intra-molecular excitations of π electrons of the anionic p-terphenyl molecules. The inter-molecular electronic excitations are much weaker and give rise to a Drude peak and a similarly weak Lorentzian band around 220 cm −1 . A dc resistivity of about 0.3 Ωcm at 300K is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. The analysis of the temperature dependence of the low-frequency response reveals a gradual decrease of the plasma frequency and the scattering rate of the Drude peak below 300K that gets anomalously enhanced below 90K. The corresponding missing spectral weight of the Drude peak appears blueshifted towards the Lorentz-band at 220 cm −1 . This characteristic blue-shift signifies an enhanced localization of the charge carriers at low temperatures and contrasts the behavior expected for a bulk superconducting state for which the missing spectral weight would be redshifted to a delta-function at zero frequency that accounts for the loss-free response of the superconducting condensate. Our data might still be compatible with a filamentary superconducting state with a volume fraction well below the percolation limit for which the spatial confinement of the condensate can result in a plasmonic resonance at finite frequency.

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“…That polyacetylene itself is probably an excitonic insulator is implied by the impressive body [16] of work on the effects of electron-electron interactions on the insulating state of the polymer. In particular, the work of Baeriswyl and his co-workers [17,18] has stressed the importance of the attractive electron-hole interaction that arises from the nearest neighbour electron-electron interaction V in the polymer. Typically, V is found to be a much larger effect than the electron-lattice interaction.…”

Section: Discussionmentioning

confidence: 99%

The excitonic ground state of the half-filled Peierls insulator

Rice¹,

Gartstein²

2005

J. Phys.: Condens. Matter

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We point out that the half-filled Peierls insulator, celebrated for its soliton excitations and its application to trans(polyacetylene), is an excitonic insulator in which collectively bound electron–hole pair excitations (excitons) are mixed into the ground state. Unlike the bound electron pairs of the Bardeen–Cooper–Schrieffer (BCS) superconductor, however, the excitonic pairs can be photoionized leading to the direct observation of the excitonic energy gap 2Δ in the optical conductivity. A deeper understanding is provided of the discovery of Kuper in 1955 of a BCS-like gap equation describing the thermodynamic properties of the Fröhlich (1954) one-dimensional charge-density-wave state.

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Theoretical Aspects of Conducting Polymers: Electronic Structure and Defect States

Cited by 17 publications

References 125 publications

The low‐lying excitation energies of polyenes investigated with a chain‐length‐dependent screened potential

The low‐lying excitation energies of polyenes investigated with a chain‐length‐dependent screened potential

Infrared ellipsometry study of the charge dynamics in K$_3$\,\!p-terphenyl

The excitonic ground state of the half-filled Peierls insulator

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