Xue Rui-Jie, Grofe Adam, Yin He, Qu Zexing, Gao Jiali, Li Hui
Institute of Theoretical Chemistry, Jilin University , 2519 Jiefang Road, Changchun 130023, People's Republic of China.
Department of Chemistry and Supercomputing Institute, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States.
J Chem Theory Comput. 2017 Jan 10;13(1):191-201. doi: 10.1021/acs.jctc.6b00733. Epub 2016 Dec 7.
Linear and two-dimensional infrared (IR) spectroscopy of site-specific probe molecules provides an opportunity to gain a molecular-level understanding of the local hydrogen-bonding network, conformational dynamics, and long-range electrostatic interactions in condensed-phase and biological systems. A challenge in computation is to determine the time-dependent vibrational frequencies that incorporate explicitly both nuclear quantum effects of vibrational motions and an electronic structural representation of the potential energy surface. In this paper, a nuclear quantum vibrational perturbation (QVP) method is described for efficiently determining the instantaneous vibrational frequency of a chromophore in molecular dynamics simulations. Computational efficiency is achieved through the use of (a) discrete variable representation of the vibrational wave functions, (b) a perturbation theory to evaluate the vibrational energy shifts due to solvent dynamic fluctuations, and (c) a combined QM/MM potential for the systems. It was found that first-order perturbation is sufficiently accurate, enabling time-dependent vibrational frequencies to be obtained on the fly in molecular dynamics. The QVP method is illustrated in the mode-specific linear and 2D-IR spectra of the H-Cl stretching frequency in the HCl-water clusters and the carbonyl stretching vibration of acetone in aqueous solution. To further reduce computational cost, a hybrid strategy was proposed, and it was found that the computed vibrational spectral peak position and line shape are in agreement with experimental results. In addition, it was found that anharmonicity is significant in the H-Cl stretching mode, and hydrogen-bonding interactions further enhance anharmonic effects. The present QVP method complements other computational approaches, including path integral-based molecular dynamics, and represents a major improvement over the electrostatics-based spectroscopic mapping procedures.
对位点特异性探针分子进行线性和二维红外（IR）光谱分析，为从分子层面了解凝聚相和生物系统中的局部氢键网络、构象动力学以及长程静电相互作用提供了契机。计算方面的一个挑战是确定随时间变化的振动频率，该频率需明确纳入振动运动的核量子效应以及势能面的电子结构表示。本文描述了一种核量子振动微扰（QVP）方法，用于在分子动力学模拟中高效确定发色团的瞬时振动频率。通过以下方式实现计算效率：（a）振动波函数的离散变量表示；（b）一种微扰理论，用于评估由于溶剂动态波动引起的振动能量位移；（c）系统的组合量子力学/分子力学势。结果发现，一阶微扰足够精确，能够在分子动力学中即时获得随时间变化的振动频率。在HCl - 水簇中H - Cl伸缩频率的模式特异性线性和二维红外光谱以及丙酮在水溶液中的羰基伸缩振动中展示了QVP方法。为进一步降低计算成本，提出了一种混合策略，结果发现计算得到的振动光谱峰位置和线形与实验结果一致。此外，还发现非谐性在H - Cl伸缩模式中很显著，并且氢键相互作用进一步增强了非谐效应。当前的QVP方法补充了其他计算方法，包括基于路径积分的分子动力学，并且相对于基于静电学的光谱映射程序有了重大改进。
