Su Neil Qiang, Xu Xin
Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Ministry of Education Key Laboratory of Computational Physical Sciences, Department of Chemistry , Fudan University , Shanghai 200433 , China.
J Phys Chem Lett. 2019 Jun 6;10(11):2692-2699. doi: 10.1021/acs.jpclett.9b01052. Epub 2019 May 10.
Vertical ionization potential (IP) and electron affinity (EA) are fundamental molecular properties, while the Δ method and the direct method are the widely used approaches to compute these properties. The Δ method is calculated by taking the total energy difference of the initial and final states, whose reliability is seriously affected by the issue associated with the imbalanced treatment of these two states. The direct method based on the derivatives involving only one single-state calculation can yield a quasi-particle spectrum whose accuracy, on the other hand, is mostly affected by the levels of approximate molecular structure theories. Because of the aforementioned issues, EA prediction can be particularly problematic. Here we present, for the first time, an analytic theory on the derivation and realization of generalized Kohn-Sham (KS) eigenvalues of doubly hybrid (DH) functionals that depend on both occupied and unoccupied orbitals. The method based on the KS eigenvalues of neutral systems, termed the NKS method, is found to suffer little from the imbalance issue, while it is only the NKS method that can offer accurate EA prediction from a good functional approximation, such as the XYG3 type of DH functionals. Being less sensitive to the size of basis sets, the NKS method is of great significance for its application to large systems. The insights gained in this work are useful for the calculation of properties associated with small energy differences while emphasizing the importance of the development of generalized functionals that rely on both occupied and unoccupied orbitals.
垂直电离势（IP）和电子亲和能（EA）是基本的分子性质，而Δ方法和直接方法是计算这些性质的广泛使用的方法。Δ方法是通过计算初始态和终态的总能量差来计算的，其可靠性受到与这两个态处理不平衡相关问题的严重影响。基于仅涉及单态计算的导数的直接方法可以产生准粒子谱，另一方面，其准确性主要受近似分子结构理论水平的影响。由于上述问题，EA预测可能特别成问题。在此，我们首次提出了一种关于双杂化（DH）泛函广义科恩-沙姆（KS）本征值的推导和实现的解析理论，该本征值依赖于占据轨道和未占据轨道。基于中性系统KS本征值的方法，称为NKS方法，发现几乎不受不平衡问题的影响，而只有NKS方法能够从良好的泛函近似（如XYG3型DH泛函）提供准确的EA预测。NKS方法对基组大小不太敏感，因此在应用于大型系统时具有重要意义。这项工作中获得的见解对于计算与小能量差相关的性质很有用，同时强调了开发依赖于占据轨道和未占据轨道的广义泛函的重要性。
