Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States.
Physical Science Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
J Chem Theory Comput. 2021 Jul 13;17(7):4195-4210. doi: 10.1021/acs.jctc.1c00412. Epub 2021 Jun 30.
For many types of vertical excitation energies, linear-response time-dependent density functional theory (LR-TDDFT) offers a useful degree of accuracy combined with unrivaled computational efficiency, although charge-transfer excitation energies are often systematically and dramatically underestimated, especially for large systems and those that contain explicit solvent. As a result, low-energy electronic spectra of solution-phase chromophores often contain tens to hundreds of spurious charge-transfer states, making LR-TDDFT needlessly expensive in bulk solution. Intensity borrowing by these spurious states can affect intensities of the valence excitations, altering electronic bandshapes. At higher excitation energies, it is difficult to distinguish spurious charge-transfer states from genuine charge-transfer-to-solvent (CTTS) excitations. In this work, we introduce an automated diabatization that enables fast and effective screening of the CTTS acceptor space in bulk solution. Our procedure introduces "natural charge-transfer orbitals" that provide a means to isolate orbitals that are most likely to participate in a CTTS excitation. Projection of these orbitals onto solvent-centered virtual orbitals provides a criterion for defining the most important solvent molecules in a given excitation and be used as an automated subspace selection algorithm for projection-based embedding of a high-level description of the CTTS state in a lower-level description of its environment. We apply this method to an molecular dynamics trajectory of I(aq) and report the lowest-energy CTTS band in the absorption spectrum. Our results are in excellent agreement with the experiment, and only one-third of the water molecules in the I(HO) simulation cell need to be described with LR-TDDFT to obtain excitation energies that are converged to <0.1 eV. The tools introduced herein will improve the accuracy, efficiency, and usability of LR-TDDFT in solution-phase environments.
对于许多类型的垂直激发能，线性响应含时密度泛函理论（LR-TDDFT）结合无与伦比的计算效率，提供了有用的准确度，尽管电荷转移激发能通常会被系统地和显著低估，尤其是对于大系统和那些包含显溶剂的系统。结果，溶液相发色团的低能电子光谱通常包含数十到数百个虚假的电荷转移态，使得 LR-TDDFT 在体相溶液中过于昂贵。这些虚假态的强度借用会影响价激发的强度，改变电子能带形状。在更高的激发能下，很难将虚假的电荷转移态与真正的电荷转移到溶剂（CTTS）激发区分开来。在这项工作中，我们引入了一种自动化的二聚化方法，能够快速有效地筛选体相溶液中的 CTTS 受体空间。我们的程序引入了“自然电荷转移轨道”，提供了一种分离最有可能参与 CTTS 激发的轨道的方法。将这些轨道投影到溶剂中心的虚拟轨道上，提供了定义给定激发中最重要溶剂分子的标准，并可作为基于投影的嵌入算法的自动子空间选择，用于在其环境的低级描述中对 CTTS 态进行高级描述。我们将此方法应用于 I(aq)的分子动力学轨迹，并报告吸收光谱中的最低能量 CTTS 带。我们的结果与实验非常吻合，仅需用 LR-TDDFT 描述 I(HO)模拟单元中的三分之一的水分子，即可获得收敛到<0.1 eV 的激发能。本文介绍的工具将提高 LR-TDDFT 在溶液相环境中的准确性、效率和可用性。
