Wong Man Tou, Cheng Yuan-Chung
Department of Chemistry and Center for Quantum Science and Engineering, National Taiwan University, Taipei City 106, Taiwan.
J Chem Phys. 2021 Apr 21;154(15):154107. doi: 10.1063/5.0042848.
We present an efficient method to simulate two-dimensional (2D) electronic spectra of condensed-phase systems with an emphasis on treating quantum nuclear wave packet dynamics explicitly. To this end, we combine a quantum Langevin equation (QLE) approach for dissipation and a perturbative scheme to calculate three-pulse photon-echo polarizations based on wave packet dynamics under the influence of external fields. The proposed dynamical approach provides a consistent description of nuclear quantum dynamics, pulse-overlap effects, and vibrational relaxation, enabling simulations of 2D electronic spectra with explicit and non-perturbative treatment of coupled electronic-nuclear dynamics. We apply the method to simulate 2D electronic spectra of a displaced-oscillator model in the condensed phase and discuss the spectral and temporal evolutions of 2D signals. Our results show that the proposed QLE approach is capable of describing vibrational relaxation, decoherence, and vibrational coherence transfer, as well as their manifestations in spectroscopic signals. Furthermore, vibrational quantum beats specific for excited-state vs ground-state nuclear wave packet dynamics can also be identified. We anticipate that this method will provide a useful tool to conduct theoretical studies of 2D spectroscopy for strong vibronically coupled systems and to elucidate intricate vibronic couplings in complex molecular systems.
我们提出了一种有效的方法来模拟凝聚相系统的二维（2D）电子光谱，重点是明确处理量子核波包动力学。为此，我们将用于耗散的量子朗之万方程（QLE）方法与基于外部场影响下的波包动力学来计算三脉冲光子回波极化的微扰方案相结合。所提出的动力学方法对核量子动力学、脉冲重叠效应和振动弛豫提供了一致的描述，能够对二维电子光谱进行明确且非微扰的电子 - 核耦合动力学模拟。我们应用该方法模拟凝聚相中位移振子模型的二维电子光谱，并讨论二维信号的光谱和时间演化。我们的结果表明，所提出的QLE方法能够描述振动弛豫、退相干和振动相干转移，以及它们在光谱信号中的表现。此外，还可以识别出特定于激发态与基态核波包动力学的振动量子拍。我们预计该方法将为开展强振动 - 电子耦合系统的二维光谱理论研究以及阐明复杂分子系统中复杂的振动 - 电子耦合提供一个有用的工具。
