Department of Chemistry, Korea University, Seoul 136-701, South Korea.
J Chem Phys. 2013 Jul 28;139(4):044111. doi: 10.1063/1.4816041.
Vibrational solvatochromic frequency shift of IR probe is an effect of interaction between local electric field and IR probe in condensed phases. Despite prolonged efforts to develop empirical maps for vibrational frequency shifts and transition dipoles of IR probes, a systematic approach to ab initio calculation of vibrational solvatochromic charges and multipoles has not been developed. Here, we report on density functional theory (DFT) calculations of N-methylacetamide (NMA) frequency shifts using implicit and coarse-grained models. The solvatochromic infrared spectral shifts are estimated based on the distributed multipole analysis of electronic densities calculated for gas-phase equilibrium structure of NMA. Thus obtained distributed solvatochromic multipole parameters are used to calculate the amide I vibrational frequency shifts of NMA in water clusters that mimic the instantaneous configurations of the liquid water. Our results indicate that the spectral shifts are primarily electrostatic in nature and can be quantitatively reproduced using the proposed model with semi-quantitative accuracy when compared to the corresponding DFT results.
振动溶剂变色红外探针的频率位移是凝聚相中原电场与红外探针相互作用的一种效应。尽管人们长期以来一直致力于开发红外探针振动频率位移和跃迁偶极子的经验图谱，但尚未开发出用于振动溶剂变色电荷和多极子的从头算系统方法。在这里，我们报告了使用隐式和粗粒模型对 N-甲基乙酰胺（NMA）频率位移的密度泛函理论（DFT）计算。基于对 NMA 气相平衡结构计算得到的电子密度的分布式多极分析来估计溶剂变色红外光谱位移。所得到的分布溶剂变色多极参数用于计算在水团簇中 NMA 的酰胺 I 振动频率位移，这些水团簇模拟了液体水的瞬时构型。我们的结果表明，光谱位移主要是静电性质的，可以使用所提出的模型以半定量的精度定量重现，与相应的 DFT 结果相比具有较高的准确性。
