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Excitonic effects in a time-dependent density functional theory.

Kirill I Igumenshchev1, Sergei Tretiak, Vladimir Y Chernyak

  • 1Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.

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|September 25, 2007
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Strongly bound excitons in one-dimensional organic semiconductors require advanced electronic structure methods. Hybrid density functionals accurately capture these many-body effects, unlike simpler approximations.

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Area of Science:

  • Computational chemistry
  • Materials science
  • Condensed matter physics

Background:

  • One-dimensional molecular materials exhibit strong many-body interactions, leading to confined excitons.
  • These excitonic effects are crucial for understanding excited state properties and cannot be ignored.

Purpose of the Study:

  • Investigate the electronic structure of one-dimensional organic semiconductors, specifically conjugated polymers.
  • Evaluate the performance of various density functional theory (DFT) functionals in describing excitonic states.

Main Methods:

  • Utilized adiabatic time-dependent density functional theory (TD-DFT).
  • Calculated lowest singlet and triplet state energies and oscillator strengths for poly(phenylenevinylene) and ladder-type poly(para-phenylene) oligomers.
  • Compared results from local density approximations, gradient-corrected functionals, and hybrid functionals.

Main Results:

  • Local density approximations and gradient-corrected functionals failed to describe bound excitonic states due to insufficient Coulomb interaction.
  • Hybrid density functionals, incorporating Hartree-Fock exchange, successfully reproduced excitonic effects.
  • Exciton sizes were found to be highly sensitive to the proportion of orbital exchange in the functionals.

Conclusions:

  • Accurate modeling of excitons in 1D organic materials necessitates advanced electronic structure methods like hybrid DFT.
  • The inclusion of nonlocal and nonadiabatic corrections is vital for capturing excitonic phenomena.
  • The degree of Hartree-Fock exchange in hybrid functionals directly influences the predicted exciton size.