Ultrafast nonadiabatic dynamics probed by nitrogen K-edge absorption spectroscopy.
Ultrafast nonadiabatic dynamics probed by nitrogen K-edge absorption spectroscopy.
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DOI：
10.1039/c9cp03019k
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发表时间：
2020-02
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通讯作者：
T. Northey;J. Norell;A. Fouda;N. Besley;M. Odelius;Thomas J Penfold
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作者：
T. Northey;J. Norell;A. Fouda;N. Besley;M. Odelius;Thomas J Penfold
X射线自由电子激光器（X-FEL）的出现使得在飞秒时间尺度上探测结构动力学成为可能。实验能力的扩展还需要理论上的同步发展，以帮助解释实验可观察值中编码的底层结构和动力学。在超快状态下，这通常需要依赖于时间的理论处理来描述超出玻恩-奥本海默近似的核动力学。在这项工作中，我们基于时间演化高斯基函数（GBF）进行量子动力学模拟，并模拟光激发吡嗪的超快X射线吸收近边结构（XANES）光谱，包括两个强耦合电子激发态和四个简正模自由度。采用两种方法来模拟激发态XANES光谱，第一种是基于多构型二阶微扰理论受限活性空间（RASPT2）方法，第二种是使用最大重叠法（MOM）和瞬态密度泛函理论（TDDFT）相结合的方法。我们证明，尽管 MOM/TDDFT 方法很简单，但它以大大减少的计算量捕获了 RASPT2 模拟的几个定性特征。然而，诸如圆锥形相交之类的特征是一个特殊的例外，因为它们需要多配置处理。对于核动力学，我们证明即使少量的 GBF 也可以对光谱可观测值提供合理的描述。这项工作为解决大型系统问题提供了重要的计算有效方法的视角。
The emergence of X-ray free electron lasers (X-FELs) has made it possible to probe structural dynamics on the femtosecond timescale. This extension of experimental capabilities also calls for a simultaneous development in theory to help interpret the underlying structure and dynamics encoded within the experimental observable. In the ultrafast regime this often requires a time-dependent theoretical treatment that describes nuclear dynamics beyond the Born-Oppenheimer approximation. In this work, we perform quantum dynamics simulations based upon time-evolving Gaussian basis functions (GBFs) and simulate the ultrafast X-ray Absorption Near-Edge Structure (XANES) spectra of photoexcited pyrazine including two strongly coupled electronically excited states and four normal mode degrees of freedom. Two methods to simulate the excited state XANES spectra are applied, the first is based upon the multi-configurational second order perturbation theory restricted active space (RASPT2) method and the second uses a combination of the maximum overlap method (MOM) and time-dependent density functional theory (TDDFT). We demonstrate that despite the simplicity of the MOM/TDDFT method, it captures several qualitative features of the RASPT2 simulations at much reduced computational effort. However, features such as the conical intersection are a particular exception as they require a multi-configurational treatment. For the nuclear dynamics, we demonstrate that even a small number of GBFs can provide reasonable description of the spectroscopic observable. This work provides perspectives for computationally efficient approaches important for addressing larger systems.