We have simulated multiexciton generation (MEG) processes in Si and Ge nanocrystals, employing the equation of motion coupled cluster single and double as a high-level ab initio approach. Simulations, consistent with the experimental results reported so far, reveal the key role of the d-polarized valence component in the chosen basis set on the accuracy and reliability of the results. Moreover, the MEG thresholds calculated with def2SVP basis set are ∼8.23(8.07) eV for seven (eight)-atom Si clusters and ∼7.58(6.84) eV for similar Ge clusters. The normalized MEG thresholds of Ge nanocrystals are 8% smaller with respect to Si. Thus, in contrast to Si, they are more appealing to the optical device designers for enhancing the device quantum efficiency. Furthermore, the resemblance of the symmetry of the simulated seven-atom clusters to those of the experimentally domelike grown nanocrystals makes the behavior of their MEG quantum probability similar.

中文翻译：

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Si和Ge纳米晶体中的多个激子产生：从头算比较研究

我们已经模拟了Si和Ge纳米晶体中的多激子产生（MEG）过程，并采用了运动耦合的单簇和双簇簇方程作为高级从头算的方法。模拟与到目前为止报道的实验结果一致，揭示了d的关键作用。-极化的价态成分在所选基础上根据结果的准确性和可靠性而定。此外，用def2SVP基集计算的MEG阈值对于七个（八个）原子的Si团簇约为8.23（8.07）eV，对于相似的Ge团簇约为7.58（6.84）eV。Ge纳米晶体的归一化MEG阈值相对于Si小8％。因此，与Si相比，它们对于提高器件量子效率的光学器件设计者更具吸引力。此外，模拟的七个原子簇的对称性与实验性圆顶状生长的纳米晶体的相似性使它们的MEG量子概率的行为相似。