有机半导体的电子电离能、亲和势和极化能的密度泛函理论研究

Density Functional Theory Studies on Ionization Energies, Electron Affinities, and Polarization Energies of Organic Semiconductors

准确预测有机半导体的能级(如电子电离能和亲和势等)对设计新型有机半导体材料和理解相关机理至关重要。从理论计算的角度看,主要挑战来自于缺少一种不仅能够在定性上合理而且在定量上精确预测,同时并不显著增加计算成本的理论方法。本文中,我们证明了通过结合极化连续介质模型(PCM)和"最优调控"区间分离密度泛函方法能够准确预测一系列有机半导体的电子电离能(IP)、亲和势(EA)和极化能,其预测结果与实验数据吻合得很好。重要的是,经过调控后分子的前线分子轨道能量(即-~εHOMO和-~εLUMO)与对应的IP和EA计算值很接近。调控方法的成功可以进一步归因于其能够根据不同分子体系或同种分子所处的不同状态(气态和固态)"最优"地平衡泛函中分别用于描述电子局域化和离域化的作用。相比而言,其它常见的密度泛函方法由于包含的HF%比例过低(如PBE)或过高(如M06HF和未调控的区间分离泛函),均不能给予合理的预测。因此,我们相信这种PCM-调控的方法能够为研究其它更加复杂的有机体系的能级问题提供一种更加可靠和便捷的理论工具。

Accurate prediction of the energy levels （i.e. ionization potential and electronic affinity） of organic semiconductors is essential for understanding related mechanisms and for designing novel organic semiconductor materials. From a theoretical point of view, a major challenge arises from the lack of a reliable method that can provide not only qualitative but also quantitative predictions at an acceptable computational cost. In this study, we demonstrate an approach, combining the polarizable continuum model （PCM） and the optimally tuned range-separated （RS） functional method, which provides the ionization potentials （IPs）, electron affinities （EAs）, and polarization energies of a series of molecular semiconductors in good agreement with available experimental values. Importantly, this tuning method can enforce the negative frontier molecular orbital energies （-εHOMO,-εLUMO） that are very close to the corresponding IPs and EAs. The success of this tuning method can be further attributed to the fact that the tuned RS functional can provide a good balance for the description of electronic localization and delocalization effects according to various molecular systems or the same molecule in different phases （i.e. gas and solid）. In comparison, other conventional functionals cannot give reliable predictions because the functionals themselves include too low （i.e. PBE） or too high （i.e. M06HF and non-tuned RS functionals） HF%. Therefore, we believe that this PCM-tuned approach represents an easily applicable and computationally efficient theoretical tool to study the energy levels of more complex organic electronic materials.