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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Vibrational Sum-Frequency Generation Spectroscopy in the Energy Representation from Dual-Level Molecular Dynamics Simulations
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Vibrational Sum-Frequency Generation Spectroscopy in the Energy Representation from Dual-Level Molecular Dynamics Simulations

机译：双层分子动力学模拟能量表示中振动和频率产生光谱

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摘要

We report a cost-effective molecular dynamics approach to calculate sum-frequency generation (SFG) vibrational spectra of molecular species at liquid interfaces in the energy representation formalism that brings together the instantaneous normal mode (INM) analysis at free-energy minima (FEM) and the dual-level free-energy perturbation (FEP) methods. This combined FEP-INM-FEM approach allows analyzing SFG spectra in terms of normal mode contributions at very-high ab initio levels, in contrast to standard time-correlation function (TCF)-based methods, from which it can be considered complementary. It is applied here to the study of the CH3-stretching band of methanol at the air-water interface, which has been thoroughly studied in the literature. The SFG band of acetonitrile in the same conditions has also been calculated with the aim of testing the capability of the method to reproduce small chemical shifts. The suitability of the proposed model is demonstrated by comparing the results with TCF data from QM/MM simulations and with experiments. Analysis of these results provides new insights into the strength and orientational dependence of the SFG signal of symmetric and asymmetric stretching vibrations of CH3 groups, which can be of paramount importance to analyze the spectra of more complex systems.
机译：我们报告了一种经济有效的分子动力学方法，以计算能量表示形式的液体界面处的分子种类的和频率产生（SFG）振动光谱，其在自由能最小值（FEM）上携带瞬时正常模式（INM）分析和双层自由能扰动（FEP）方法。这种组合的FEP-INM-FEM方法允许在非常高的AB Initio级别的正常模式贡献中分析SFG光谱，与标准时间相关函数（TCF）的基础方法相比，可以考虑互补的方法。这里应用于在空气 - 水界面处研究了甲醇的CH3拉伸带的研究，该甲醇在文献中已经彻底研究。同样条件下的乙腈的SFG带也旨在测试该方法再现小化学班次的能力。通过将来自QM / MM模拟的TCF数据和实验进行比较来证明所提出的模型的适用性。这些结果的分析为CH3组的对称和不对称拉伸振动的SFG信号的强度和取向依赖性提供了新的洞察，这可以是分析更复杂系统的光谱的至关重要的。

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