Zhou Ruiyi, Kanai Yosuke
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
J Chem Phys. 2021 Feb 7;154(5):054107. doi: 10.1063/5.0035435.
We expand the concept of natural transition orbitals in the context of real-time time-dependent density functional theory (RT-TDDFT) and show its application in practical calculations. Kohn-Sham single-particle wavefunctions are propagated in RT-TDDFT simulation, and physical properties remain invariant under their unitary transformation. In this work, we exploit this gauge freedom and expand the concept of natural transition orbitals, which is widely used in linear-response TDDFT, for obtaining a particle-hole description in RT-TDDFT simulation. While linear-response TDDFT is widely used to study electronic excitation, RT-TDDFT can be employed more generally to simulate non-equilibrium electron dynamics. Studying electron dynamics in terms of dynamic transitions of particle-hole pairs is, however, not straightforward in the RT-TDDFT simulation. By constructing natural transition orbitals through projecting time-dependent Kohn-Sham wave functions onto occupied/unoccupied eigenstate subspaces, we show that linear combinations of a pair of the resulting hole/particle orbitals form a new gauge, which we refer to as dynamical transition orbitals. We demonstrate the utility of this framework to analyze RT-TDDFT simulations of optical excitation and electronic stopping dynamics in the particle-hole description.
我们在实时含时密度泛函理论（RT - TDDFT）的背景下扩展了自然跃迁轨道的概念，并展示了其在实际计算中的应用。在RT - TDDFT模拟中，科恩 - 沈单粒子波函数随时间演化，并且其物理性质在酉变换下保持不变。在这项工作中，我们利用这种规范自由度，扩展了在线性响应TDDFT中广泛使用的自然跃迁轨道的概念，以便在RT - TDDFT模拟中获得粒子 - 空穴描述。虽然线性响应TDDFT广泛用于研究电子激发，但RT - TDDFT可更普遍地用于模拟非平衡电子动力学。然而，在RT - TDDFT模拟中，从粒子 - 空穴对的动态跃迁角度研究电子动力学并非易事。通过将含时科恩 - 沈波函数投影到占据/未占据本征态子空间来构建自然跃迁轨道，我们表明一对所得空穴/粒子轨道的线性组合形成了一种新的规范，我们将其称为动态跃迁轨道。我们展示了该框架在粒子 - 空穴描述中分析光激发和电子阻止动力学的RT - TDDFT模拟的效用。
