Do we need delocalised wavefunctions for the excited state dynamics of 1,1-difluoroethylene?
Do we need delocalised wavefunctions for the excited state dynamics of 1,1-difluoroethylene?
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DOI：
10.1139/cjc-2022-0267
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发表时间：
2023-02
影响因子：
1.1
通讯作者：
Sandra G'omez;N. Singer;L. Gonz'alez;G. Worth
中科院分区：
文献类型：
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作者：
Sandra G'omez;N. Singer;L. Gonz'alez;G. Worth
在这项工作中，我们建立了一个模型哈密顿研究激发态量子动力学的1，1-二氟乙烯，一个分子，具有等价的原子交换的扭转对称操作导致等效的势能面上的最小值。在具有许多自由度的系统中，最小能量几何不是唯一的，基态波函数将在多个最小值之间离域。在这个小的测试系统中，我们探测激发态动力学考虑本地化（在一个单一的最小值）和离域（分散在多个最小值）波函数，并检查这种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括7个电子态，包括价态和里德伯态，计算与MS-CASPT 2方法和投影到1，1-二氟乙烯在其振动基态的12个正常模式的振动坐标。该哈密顿量沿扭转自由度沿着对称化，以使两个最小值完全等效，并且该模型与实验吸收光谱的良好一致性支持。量子动力学的结果表明，不同的初始条件研究并没有明显影响的激发态的人口或吸收光谱的动力学模拟时，假设一个三角洲脉冲激发。未来的工作将着眼于是否可以形成初始叠加，引导系统，例如，一个单一的最小值。
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. Future work will look at whether initial superpositions can be formed that guide the system, e.g. to a single minimum.