研究1,1-二氟乙烯的激发态动力学是否需要离域波函数？
Do we need delocalised wavefunctions for the excited state dynamics of 1,1-difluoroethylene?
AI总结：
本文构建含七个电子态、十二个简正模并经扭转轴对称化的1,1-二氟乙烯模型哈密顿量，比较局域与离域初始波函数，证明delta脉冲下二者的激发态布居和吸收光谱基本无差异。
摘要：
在本工作中，我们建立了一个模型哈密顿量，以研究1,1-二氟乙烯的激发态量子动力学；该分子具有可通过扭转对称操作互换的等价原子，从而在势能面上产生等价极小值。在具有许多自由度且最低能量几何结构不唯一的体系中，基态波函数将在多个极小值之间离域。在这个小型测试体系中，我们分别考察采用局域化（位于单个极小值内）和离域化（分布于多个极小值之间）波函数时的激发态动力学，并检验这一选择是否会影响量子动力学计算的最终结果。我们的分子哈密顿量包含七个电子态，其中有价态和Rydberg态；这些电子态采用MS-CASPT2方法计算，并投影到1,1-二氟乙烯振动基态的十二个简正模的振动坐标上。该哈密顿量已沿扭转自由度进行对称化，使两个极小值完全等价；模型与实验吸收光谱之间的极好一致性为其提供了支持。量子动力学结果表明，在假设delta脉冲激发来模拟动力学时，所研究的不同初始条件并不会显著影响激发态布居或吸收光谱。
英文摘要：
In this work we set up a model Hamiltonian to study the excited state quantum dynamics of 1,1-difluoroethylene, a molecule that has equivalent atoms exchanged by a torsional symmetry operation leading to equivalent minima on the potential energy surface. In systems with many degrees of freedom where the minimum energy geometry is not unique, the ground state wavefunction will be delocalised among multiple minima. In this small test system, we probe the excited state dynamics considering localised (in a single minimum) and delocalised (spread over among multiple minima) wavefunctions and check whether this choice would influence the final outcome of the quantum dynamics calculations. Our molecular Hamiltonian comprises seven electronic states, including valence and Rydberg states, computed with the MS-CASPT2 method and projected onto the vibrational coordinates of the twelve normal modes of 1,1-difluoroethylene in its vibrational ground state. This Hamiltonian has been symmetrised along the torsional degree of freedom to make both minima completely equivalent and the model is supported by the excellent agreement with the experimental absorption spectrum. Quantum dynamics results show that the different initial conditions studied do not appreciably affect the excited state populations or the absorption spectrum when the dynamics is simulated assuming a delta pulse excitation.
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