Winslow Max, Cross Warren B, Robinson David
Department of Chemistry and Forensics, School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom.
J Chem Theory Comput. 2020 May 12;16(5):3253-3263. doi: 10.1021/acs.jctc.9b00917. Epub 2020 May 4.
Determining conical intersection geometries is of key importance to understanding the photochemical reactivity of molecules. While many small- to medium-sized molecules can be treated accurately using multireference approaches, larger molecules require a less computationally demanding approach. In this work, minimum energy crossing point conical intersection geometries for a series of molecules have been studied using spin-flip TDDFT (SF-TDDFT), within the Tamm-Dancoff Approximation, both with and without explicit calculation of nonadiabatic coupling terms, and compared with both XMS-CASPT2 and CASSCF calculated geometries. The less computationally demanding algorithms, which do not require explicit calculation of the nonadiabatic coupling terms, generally fare well with the XMS-CASPT2 reference structures, while the relative energetics are only reasonably replicated with the MECP structure as calculated with the BHHLYP functional and full nonadiabatic coupling terms. We also demonstrate that, occasionally, CASSCF structures deviate quantitatively from the XMS-CASPT2 structures, showing the importance of including dynamical correlation.
确定锥形交叉几何结构对于理解分子的光化学反应性至关重要。虽然许多中小分子可以使用多参考方法进行精确处理，但较大的分子需要一种计算要求较低的方法。在这项工作中，使用自旋翻转TDDFT（SF-TDDFT），在Tamm-Dancoff近似下，对一系列分子的最低能量交叉点锥形交叉几何结构进行了研究，同时考虑了有无非绝热耦合项的显式计算，并与XMS-CASPT2和CASSCF计算的几何结构进行了比较。计算要求较低的算法，即不需要显式计算非绝热耦合项的算法，通常与XMS-CASPT2参考结构吻合良好，而相对能量仅与使用BHHLYP泛函和完整非绝热耦合项计算的MECP结构合理匹配。我们还证明，偶尔CASSCF结构会与XMS-CASPT2结构产生定量偏差，这表明包含动态相关的重要性。
