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Adiabatic Switching Extended To Prepare Semiclassically Quantized Rotational–Vibrational Initial States for Quasiclassical Trajectory Calculations
The Journal of Physical Chemistry Letters ( IF 5.7 ) Pub Date : 2017-09-13 00:00:00 , DOI: 10.1021/acs.jpclett.7b01838
Tibor Nagy 1 , György Lendvay 1, 2
Affiliation  

An approximation-free adiabatic switching method to generate semiclassically quantized ensembles of rovibrational states of polyatomic molecules for use as initial conditions in quasiclassical trajectory calculations is presented. Vibrational states are prepared, starting from an ensemble of classical states corresponding to the desired quantum state of the normal-mode Hamiltonian by slowly switching on the anharmonicity in internal coordinates, thereby avoiding rotational contamination. To generate rovibrational states, an extension is proposed: The vibrationally quantized molecules are slowly spun up to the desired quantized angular momentum. The ensembles obtained with adiabatic switching for CH4 are insensitive to the choice of internal coordinates and stationary; furthermore, their mean energies agree remarkably well with the quantum mechanical values: The zero-point energy and 15 vibrational levels of the first three polyads are within 20 cm–1, the rotational levels are between J = 1 and 50 within 1%, and the standard deviation is always <1%. Adiabatic switching produces classical state ensembles with significantly better properties than normal-mode sampling, making them more appropriate in quasiclassical trajectory calculations.

中文翻译:

绝热切换扩展为准经典弹道计算准备半经典量化的旋转振动初始状态

提出了一种近似的无绝热转换方法,以生成多原子分子振动状态的半经典量化合奏,用作准经典轨迹计算的初始条件。通过缓慢地切换内部坐标中的非谐性,从与正态模态哈密顿量的所需量子态相对应的经典态的整体开始,准备振动态,从而避免了旋转污染。为了产生振动状态,提出了一种扩展:将振动量化的分子缓慢旋转到所需的量化角动量。通过CH 4的绝热切换获得的合奏对内部坐标和固定点的选择不敏感;此外,它们的平均能量与量子力学值非常吻合:前三个多单元的零点能量和15个振动水平在20 cm –1以内,旋转水平在J = 1至50之间在1%以内,并且标准偏差始终<1%。绝热切换产生的经典状态合奏具有比正常模式采样好得多的特性,从而使其更适合于准经典轨迹计算。
更新日期:2017-09-13
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