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arXiv 0802.3168cond-mat.mtrl-sci
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分子晶体中的光谱和交换相关效应

Optical spectra and exchange-correlation effects in molecular crystals

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

摘要:

采用第一性原理GW-Bethe Salpeter方程和量子Monte Carlo方法计算了红荧烯(C $_{42}$ H $_{28}$)分子和晶体的光学和电子性质.多体效应控制着分子晶体的光谱和准粒子带隙。我们解释所观察到的红荧烯微晶的黄绿色光致发光的结果形成的分子间,电荷转移自旋单重态激子。相反,自旋三重态激子是局域的,并且在光谱的红端具有预测的磷光。我们发现,交换能在提高分子内自旋单重态激子的能量高于分子间激子的能量中起着重要的作用。预测激子结合能为约0.5 eV(自旋单线态)至1 eV(自旋三线态)。计算的电子能隙为2.8 eV。理论吸收光谱与最近的椭偏测量数据吻合得很好。

英文摘要:

We report first-principles GW-Bethe Salpeter Equation and Quantum Monte Carlo calculations of the optical and electronic properties of molecular and crystalline rubrene (C$_{42}$H$_{28}$). Many-body effects dominate the optical spectrum and quasi-particle 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.

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