Optical spectra and exchange-correlation effects in molecular crystals

Na Sai, Murilo L. Tiago, James R. Chelikowsky, Fernando A. Reboredo

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    78 Scopus citations

    Abstract

    We report the first-principles GW -Bethe-Salpeter equation and quantum Monte Carlo calculations of the optical and electronic properties of molecular and crystalline rubrene (C42 H28). Many-body effects dominate the optical spectrum and quasiparticle gap of molecular crystals. We interpret the observed yellow-green photoluminescence in rubrene microcrystals as a result of the formation of intermolecular, charge-transfer, spin-singlet excitons. In contrast, spin-triplet excitons are localized and intramolecular with a predicted phosphorescence at the red end of the optical spectrum. We find that the exchange energy plays a fundamental role in raising the energy of intramolecular spin-singlet excitons above the intermolecular ones. Exciton binding energies are predicted to be around 0.5 eV (spin singlet) to 1 eV (spin triplet). The calculated electronic gap is 2.8 eV. The theoretical absorption spectrum agrees very well with recent ellipsometry data.

    Original languageEnglish
    Article number161306
    JournalPhysical Review B - Condensed Matter and Materials Physics
    Volume77
    Issue number16
    DOIs
    StatePublished - Apr 30 2008

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