Nagy Tibor, Lendvay György
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar tudósok körútja 2, H-1117 Budapest, Hungary.
Department of General and Inorganic Chemistry, University of Pannonia , Egyetem u. 10, H-8800 Veszprém, Hungary.
J Phys Chem Lett. 2017 Sep 21;8(18):4621-4626. doi: 10.1021/acs.jpclett.7b01838. Epub 2017 Sep 13.
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 CH 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, 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.
提出了一种无近似的绝热切换方法，用于生成多原子分子振转态的半经典量子化系综，以用作准经典轨迹计算的初始条件。通过缓慢开启内坐标中的非谐性，从对应于简正模式哈密顿量所需量子态的经典态系综开始制备振动态，从而避免转动污染。为了生成振转态，提出了一种扩展方法：将振动量子化的分子缓慢加速到所需的量子化角动量。通过绝热切换获得的CH系综对内坐标的选择不敏感且稳定；此外，它们的平均能量与量子力学值非常吻合：前三个多组的零点能量和15个振动态在20 cm范围内，转动能级在J = 1到50之间，误差在1%以内，标准差始终<1%。绝热切换产生的经典态系综具有比简正模式采样显著更好的性质，使其在准经典轨迹计算中更合适。
