Electrostatic DFT map for the complete vibrational amide band of NMA
Electrostatic DFT map for the complete vibrational amide band of NMA
复制标题
DOI：
10.1021/jp0523241
复制
发表时间：
2005-11-03
影响因子：
2.9
通讯作者：
Mukamel, S
中科院分区：
文献类型：
--
作者：
Hayashi, T;Zhuang, W;Mukamel, S
在DFT(BPW91/6-31G(d，p))水平上计算了N-甲基乙酰胺(NMA)的酰胺I、II、III和A模的非简谐振动哈密顿量。NMA几何构型与用该哈密顿量计算的酰胺频率涨落以及TIP3水中分子动力学模拟得到的波动溶剂电场之间存在很强的相关性。酰胺I和A的频率与C=O和N-H键长呈显著正相关。C=O和C-N酰胺键长度呈负相关，表明溶剂引起的两性离子共振贡献的波动。为了进行精确的红外线型模拟，需要对跃迁电荷密度(TCDs)整个区域内的全局电场进行采样。报道了代表酰胺基态和泛色态10个最低态涨落的集体静电溶剂坐标。对NMA-3H(2)O团簇的简正模分析表明，在酰胺模的频率自相关函数中发现的660 cm(-1)到1100 cm(-1)的振荡可归因于分子间氢键与NMA的酰胺氧的两次弯曲振动。
An anharmonic vibrational Hamiltonian for the amide I, II, III, and A modes of N-methyl acetamide (NMA), recast in terms of the 19 components of an external electric field and its first and second derivative tensors (electrostatic DFT map), is calculated at the DFT(BPW91/6-31G(d,p)) level. Strong correlations are found between NMA geometry and the amide frequency fluctuations calculated using this Hamiltonian together with the fluctuating solvent electric field obtained from the MD simulations in TIP3 water. The amide I and A frequencies are strongly positively correlated with the C=O and N-H bond lengths. The C=O and C-N amide bond lengths are negatively correlated, suggesting the solvent-induced fluctuations of the contribution of zwitterionic resonance form. Sampling the global electric field in the entire region of the transition charge densities (TCDs) is required for accurate infrared line shape simulations. Collective electrostatic solvent coordinates which represent the fluctuations of the 10 lowest amide fundamental and overtone states are reported. Normal-mode analysis of an NMA-3H(2)O cluster shows that the 660 cm(-1) to 1100 cm(-1) oscillation found in the frequency autocorrelation functions of the amide modes may be ascribed to the two bending vibrations of intermolecular hydrogen bonds with the amide oxygen of NMA.