Predicting Intersystem Crossing Rates with AIMS-DFT Molecular Dynamics,The Journal of Physical Chemistry A

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Predicting Intersystem Crossing Rates with AIMS-DFT Molecular Dynamics
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2018-03-13 00:00:00 , DOI: 10.1021/acs.jpca.8b00883
Dmitry A. Fedorov ₁ , Aleksandr O. Lykhin _{1,

2} , Sergey A. Varganov ₁

Affiliation

Accurate prediction of the intersystem crossing rates is important for many different applications in chemistry, physics, and biology. Recently, we implemented the ab initio multiple spawning (AIMS) molecular dynamics method to describe the intersystem crossing processes, where nonradiative transitions between electronic states with different spin multiplicities are mediated by spin–orbit coupling. Our original implementation of the direct AIMS dynamics used the complete active space self-consistent field (CASSCF) method to describe multiple coupled electronic states on which multidimensional Gaussian wave packets were propagated. In this work, we improve the computational efficiency and versatility of the AIMS dynamics by interfacing it with the density functional theory (DFT). The new AIMS-DFT and the earlier AIMS-CASSCF implementations are used to investigate the effects of electronic structure methods on the predicted intersystem crossing rate constants and the lowest triplet state lifetime in the GeH₂ molecule. We also compare the rates and lifetimes obtained from the AIMS simulations with those predicted by the statistical nonadiabatic transition state theory (NA-TST). In NA-TST, the probabilities of spin transitions are calculated using the Landau–Zener, weak coupling, and Zhu–Nakamura formulas. Convergence of the AIMS rate constants with respect to the simulation time and the number of initial trajectories (Gaussian wave packets) is analyzed. An excellent agreement between AIMS-DFT and AIMS-CASSCF can be explained by cancelation of two effects: higher energy barriers and a stronger spin–orbit coupling in DFT relative to CASSCF. The rate constants obtained with the AIMS-DFT dynamics are about a factor of 2 larger than those predicted by the statistical NA-TST. This is likely due to the importance of the nonlocal interstate transitions missing from the NA-TST description.

中文翻译：

使用AIMS-DFT分子动力学预测系统间交叉速率

系统间交叉速率的准确预测对于化学，物理和生物学中的许多不同应用都很重要。最近，我们实现了从头开始多重生成（AIMS）分子动力学方法来描述系统间交叉过程，其中具有不同自旋多重性的电子态之间的非辐射跃迁是通过自旋-轨道耦合来介导的。我们对直接AIMS动力学的最初实现使用完整的有源空间自洽场（CASSCF）方法来描述多维高斯波包在其上传播的多个耦合电子状态。在这项工作中，我们通过与密度泛函理论（DFT）进行接口来提高AIMS动力学的计算效率和通用性。_2个分子。我们还将AIMS模拟获得的速率和寿命与统计非绝热过渡态理论（NA-TST）预测的速率和寿命进行比较。在NA-TST中，使用Landau-Zener，弱耦合和Zhu-Nakamura公式来计算自旋跃迁的概率。分析了AIMS速率常数相对于仿真时间和初始轨迹数（高斯波包）的收敛性。AIMS-DFT和AIMS-CASSCF之间的极好的协议可以通过抵消两个效应来解释：相对于CASSCF，更高的能垒和DFT中更强的自旋轨道耦合。通过AIMS-DFT动态获得的速率常数比通过统计NA-TST预测的速率常数大大约2倍。

更新日期：2018-03-13

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