Stella Martina, Thapa Kritam, Genovese Luigi, Ratcliff Laura E
Department of Materials, Imperial College London, London SW7 2AZ, U.K.
The Abdus Salam International Centre for Theoretical Physics, Condensed Matter and Statistical Physics, Trieste 34151, Italy.
J Chem Theory Comput. 2022 May 10;18(5):3027-3038. doi: 10.1021/acs.jctc.1c00548. Epub 2022 Apr 26.
Despite the variety of available computational approaches, state-of-the-art methods for calculating excitation energies, such as time-dependent density functional theory (TDDFT), are computationally demanding and thus limited to moderate system sizes. Here, we introduce a new variation of constrained DFT (CDFT), wherein the constraint corresponds to a particular transition (T), or a combination of transitions, between occupied and virtual orbitals, rather than a region of the simulation space as in traditional CDFT. We compare T-CDFT with TDDFT and ΔSCF results for the low-lying excited states (S and T) of a set of gas-phase acene molecules and OLED emitters and with reference results from the literature. At the PBE level of theory, T-CDFT outperforms ΔSCF for both classes of molecules, while also proving to be more robust. For the local excitations seen in the acenes, T-CDFT and TDDFT perform equally well. For the charge transfer (CT)-like excitations seen in the OLED molecules, T-CDFT also performs well, in contrast to the severe energy underestimation seen with TDDFT. In other words, T-CDFT is equally applicable to both local excitations and CT states, providing more reliable excitation energies at a much lower computational cost than TDDFT cost. T-CDFT is designed for large systems and has been implemented in the linear-scaling BigDFT code. It is therefore ideally suited for exploring the effects of explicit environments on excitation energies, paving the way for future simulations of excited states in complex realistic morphologies, such as those which occur in OLED materials.
尽管有各种各样的可用计算方法，但用于计算激发能的最先进方法，如含时密度泛函理论（TDDFT），计算量很大，因此仅限于中等系统规模。在这里，我们引入了一种受限密度泛函理论（CDFT）的新变体，其中约束对应于占据轨道和虚拟轨道之间的特定跃迁（T）或跃迁组合，而不是传统CDFT中的模拟空间区域。我们将T-CDFT与一组气相并苯分子和OLED发光体的低激发态（单重态和三重态）的TDDFT和ΔSCF结果以及文献中的参考结果进行了比较。在PBE理论水平下，对于这两类分子，T-CDFT都优于ΔSCF，同时也证明更稳健。对于并苯中出现的局域激发，T-CDFT和TDDFT表现同样出色。对于OLED分子中类似电荷转移（CT）的激发，T-CDFT也表现良好，这与TDDFT严重低估能量形成对比。换句话说，T-CDFT同样适用于局域激发和CT态，以比TDDFT低得多的计算成本提供更可靠的激发能。T-CDFT是为大系统设计的，并且已经在具有线性标度的BigDFT代码中实现。因此，它非常适合探索显式环境对激发能的影响，为未来模拟复杂实际形态（如OLED材料中出现的形态）中的激发态铺平了道路。
