Solitons and polarons in polyacetylene: Self-consistent-field calculations of the effect of neutral and charged defects on molecular geometry

Boudreaux, D. S.; Chance, R. R.; Brédas, Jean Luc; Silbey, R.

doi:10.1103/physrevb.28.6927

Cited by 168 publications

(63 citation statements)

References 40 publications

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“…The results of these analytical studies have also been confirmed by numerous computer simulations of discrete systems [12]. Some indirect experimental evidence of soliton's (large polaron's) existence in quasi-one-dimensional systems have been reported in [48][49][50][51][52][53][54][55][56].…”

Section: Hamiltonian Of the System And Dynamic Equationssupporting

confidence: 52%

Donor-acceptor electron transport mediated by solitons

2014

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Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We study the long-range electron and energy transfer mediated by solitons in a quasi-one-dimensional molecular chain (conjugated polymer, alpha-helical macromolecule, etc.) weakly bound to a donor and an acceptor. We show that for certain sets of parameter values in such systems an electron, initially located at the donor molecule, can tunnel to the molecular chain, where it becomes self-trapped in a soliton state, and propagates to the opposite end of the chain practically without energy dissipation. Upon reaching the end, the electron can either bounce back and move in the opposite direction or, for suitable parameter values of the system, tunnel to the acceptor. We estimate the energy efficiency of the donor-acceptor electron transport depending on the parameter values. Our calculations show that the soliton mechanism works for the parameter values of polypeptide macromolecules and conjugated polymers. We also investigate the donor-acceptor electron transport in thermalized molecular chains.

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Section: Hamiltonian Of the System And Dynamic Equationssupporting

confidence: 52%

Donor-acceptor electron transport mediated by solitons

2014

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“…For systems longer than C 41 H 43 , MP2 becomes prohibitively expensive, and DFT-hybrid geometries can be used without loss of accuracy. For example in Figure 3 Since more localized defects are obtained with HF, MP2/ 6-31G, and with semiempirical methods 7,16,20,23,29,35 and since forces during the geometry optimizations are very small, it seemed plausible that the differences are caused by very flat potential energy surfaces rather than the failure of certain methods. To investigate how big the energy lowering due to localization is, the counterions were removed, and single point energies were calculated on the geometries optimized in the presence of counterions.…”

Section: Methodsmentioning

confidence: 99%

“…[16][17][18] Theoretical calculations, mostly employing semiempirical and Hartree-Fock methods, have confirmed the presence of self-localization in the presence and in the absence of counterions. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] At higher levels of theory, the size of the defects in the absence of counterions tends to increase 35 and bipolarons become unstable with respect to two polarons. [36][37][38] As an alternative to bipolaron formation, π-dimers of radical cations have been shown to be stable when solvent effects are included in the theoretical treatment.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene

Salzner

2006

J. Chem. Theory Comput.

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Electronic excitations of polyene cations with chain lengths of up to 101 CH units were investigated as model systems for lightly doped polyacetylene (PA). Since high level ab initio calculations such as complete active space perturbation theory (CASPT2) are limited to systems with about 14 CH units, the performances of time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) were evaluated. It turned out that TDDFT excitations energies are much more accurate for polyene cations than for neutral polyenes. The difference between TDHF and TDDFT excitation energies for the first allowed excited state of C 49 H 51 + is only 0.30 eV with pure DFT and 0.21 eV with a hybrid functional. For open-shell systems, pure DFT is found to be superior to DFT-hybrid functionals because it does not suffer from spin-contamination. Pure TDDFT excitation energies and oscillator strengths for small openshell polyene cations compare well with high level ab initio results. Excitation energies are found to be almost independent of the geometry, i.e., the size of the defect. Localization of the defect, however, shifts oscillator strengths from the HOMO-LUMO transition to higher lying excited states of the same symmetry. Lightly doped PA is predicted to exhibit several strong absorptions below 1 eV.

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“…Polyacetylene, (CH) x , is the only known polymer with a degenerate ground state due to its access to two possible configurations as shown in Figure 3 The two structures differ from each other by the position of carbon-carbon single and double bonds. While polyacetylene can exist in two isomeric forms: cis and transpolyacetylene, the trans-acetylene form is thermodynamically more stable and the cis-trans isomerization is irreversible [36]. A soliton can also be viewed as an excitation of the radical from one potential well to another well of the same energy (Figure 3 degenerate polyacetylene).…”

Section: Mechanism Of Conductivitymentioning

confidence: 99%

“…A neutral soliton occurs in pristine trans-polyacetylene when a chain contains an odd number of conjugated carbons, in which case there remains an unpaired π-electron, a radical, which corresponds to a soliton ( Figure 4). In a long chain, the spin density in a neutral soliton (or charge density in a charged soliton) is not localized on one carbon but spread over several carbons [36,37] which gives the soliton a width. Starting from one side of the soliton, the double bonds become gradually longer and the single bonds shorter, so that arriving at the other side, the alternation has completely reversed.…”

Section: Mechanism Of Conductivitymentioning

confidence: 99%