Classical, Thermostated Ring Polymer, and Quantum VSCF/VCI Calculations of IR Spectra of H7O3+ and H9O4+ (Eigen) and Comparison with Experiment,The Journal of Physical Chemistry A

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Classical, Thermostated Ring Polymer, and Quantum VSCF/VCI Calculations of IR Spectra of H7O3+ and H9O4+ (Eigen) and Comparison with Experiment
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2019-01-18 00:00:00 , DOI: 10.1021/acs.jpca.8b11603
Qi Yu ₁ , Joel M. Bowman ₁

Affiliation

We report vibrational IR spectra of the protonated water clusters H₇O₃⁺ and H₉O₄⁺ (Eigen) in the range from 0 to 4000 cm^–1, from classical molecular dynamics (MD) and thermostated ring polymer molecular dynamics (TRPMD) calculations, using recent high-level ab initio potential and dipole moments surfaces. The MD spectra are done at 20 and 100 K, whereas the computationally intensive TRPMD spectra are done at 100 K. These spectra are compared with previous quantum vibrational self-consistent field/virtual state configuration interaction (VSCF/VCI) and quasi-classical MD calculations, using the same potential and dipole moment surfaces, and with experimental spectra for cold (∼20 K) clusters. As expected, the 20 K MD spectra have vibrational bands close to the harmonic ones, and at 100 K some downshifting of the bands is seen along with significant broadening. The TRPMD calculations, using two different thermostats (path integral Langevin equation and generalized Langevin Equation thermostat), show substantial downshifting relative to the classical spectrum at 100 K, especially for the intense proton-stretch bands. However, the downshifting is not sufficient to produce quantitative agreement with the VSCF/VCI (and experimental) band positions. An analysis of these positions is given based on a previously reported linear correlation between the hydronium O–H bond length and the harmonic frequency.

中文翻译：

H ₇ O ₃⁺和H ₉ O ₄⁺（本征）的红外光谱的经典，恒温环聚合物和量子VSCF / VCI计算以及与实验的比较

我们报告了质子化水簇H ₇ O ₃⁺和H ₉ O ₄⁺（本征）在0到4000 cm ^–1范围内的振动红外光谱。，从经典分子动力学（MD）和恒温环聚合物分子动力学（TRPMD）计算，使用最近的高水平从头算势和偶极矩表面进行。MD光谱在20和100 K下完成，而计算密集型TRPMD光谱在100 K下完成。将这些光谱与先前的量子振动自洽场/虚拟状态配置相互作用（VSCF / VCI）和准经典MD进行比较使用相同的电势和偶极矩表面以及冷（〜20 K）团簇的实验光谱进行计算。正如预期的那样，20 K MD光谱的振动带接近谐波，而在100 K处，该带的一些下移以及明显的展宽。TRPMD计算使用两个不同的恒温器（路径积分Langevin方程和广义Langevin方程恒温器），相对于100 K下的经典谱，显示出大幅降档，尤其是对于强质子拉伸带而言。但是，降档不足以产生与VSCF / VCI（和实验）波段位置的定量一致性。根据先前报道的水合氢键氢键长度与谐波频率之间的线性相关性，对这些位置进行了分析。

更新日期：2019-01-18

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