Ramos Pablo, Pavanello Michele
Department of Chemistry, Rutgers University, Newark, New Jersey 07102, USA.
J Chem Phys. 2021 Jan 7;154(1):014110. doi: 10.1063/5.0028872.
Excited Costrained Density Functional Theory (XCDFT) [Ramos and Pavanello, J. Chem. Phys. 148, 144103 (2018)] is a variational excited state method that extends ground state DFT to the computation of low-lying excited states. It borrows much of the machinery of Constrained DFT (CDFT) with a crucial difference: the constraint imposes a population of one electron in the Hilbert space spanned by the virtuals of a reference ground state. In this work, we present theory and implementation for evaluating nonadiabatic coupling vectors (NACVs) between the first excited state computed with XCDFT and the ground state. Our NACVs are computed analytically using density functional perturbation theory with a formalism that is general enough that could be applied to CDFT diabatic states. We showcase the new method with pilot NACV calculations for the conical intersection in H, the avoided crossing in selenoacrolein, and the NACV magnitudes in azobenzene. Despite complications from the nonorthogonality of the wavefunctions, XCDFT's energy surfaces and NACVs reproduce benchmark values and respect known sum rules within a reasonable degree. This shows that XCDFT is a viable method for nonadiabatic dynamics simulations.
激发约束密度泛函理论（XCDFT）[拉莫斯和帕瓦内洛，《化学物理杂志》148, 144103 (2018)] 是一种变分激发态方法，它将基态密度泛函理论扩展到低激发态的计算。它借鉴了许多约束密度泛函理论（CDFT）的机制，但有一个关键区别：该约束在由参考基态的虚拟轨道所张成的希尔伯特空间中强制一个电子占据。在这项工作中，我们给出了用于评估用XCDFT计算的第一激发态与基态之间的非绝热耦合矢量（NACV）的理论和实现方法。我们的NACV使用密度泛函微扰理论通过一种形式解析计算，该形式足够通用，可应用于CDFT绝热态。我们通过对H中的锥形交叉、硒代丙烯醛中的避免交叉以及偶氮苯中的NACV大小进行初步NACV计算来展示这种新方法。尽管波函数非正交会带来复杂性，但XCDFT的能量曲面和NACV在合理程度上重现了基准值并符合已知的求和规则。这表明XCDFT是一种用于非绝热动力学模拟的可行方法。
