Copeland Christopher, Menon Omkaran, Majumdar D, Roszak Szczepan, Leszczynski Jerzy
Interdisciplinary Center for Nanotoxicity, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217, USA.
Phys Chem Chem Phys. 2017 Sep 20;19(36):24866-24878. doi: 10.1039/c7cp04224h.
Low-frequency vibrations coupled to high-frequency modes are known to influence the hydrogen bond strengths in a weakly interacting dimer. In this context, various acetic acid and acetamide dimers were analyzed using Møller-Plesset second-order perturbation (MP2) and density functional theory (DFT)-based approaches with explicit anharmonicity corrections. The computed low-frequency fundamentals as well as the high-frequency modes, which were found to be related to hydrogen bonding (OH/NH stretching modes), were analyzed and their computed intensities were correlated with their hydrogen-bond strengths/binding energies. There are similarities in the nature of eight low-frequency fundamentals of these two dimers, and the in-plane bending and stretch-bend fundamentals of the different dimers of these two species (in this low-frequency region) have specific roles in their relative stability order. The computed linear correlations were further verified against the results from coupled cluster calculations including triple excitation (CCSD(T)), Gaussian-G4 (G4), Gaussian-G2-MP2 (G2MP2) and complete basis set (CBS-QB3) methods of high accuracy energy calculations. As a consequence of such linear correlations, an additive property of local fragment energies (responsible for hydrogen bonding) was found to be a valid approximation to predict the binding energies of such dimers and the idea was found to be extendable to the other homologues of these acids/amides.
已知与高频模式耦合的低频振动会影响弱相互作用二聚体中的氢键强度。在此背景下，使用基于Møller-Plesset二阶微扰（MP2）和密度泛函理论（DFT）的方法，并进行显式非谐性校正，对各种乙酸和乙酰胺二聚体进行了分析。分析了计算得到的低频基频以及与氢键（OH/NH伸缩模式）相关的高频模式，并将其计算强度与其氢键强度/结合能相关联。这两种二聚体的八个低频基频性质存在相似性，并且这两种物质不同二聚体的面内弯曲和伸缩弯曲基频（在该低频区域）在其相对稳定性顺序中具有特定作用。针对包括三重激发的耦合簇计算（CCSD(T)）、高斯-G4（G4）、高斯-G2-MP2（G2MP2）和高精度能量计算的完全基组（CBS-QB3）方法的结果，进一步验证了计算得到的线性相关性。由于这种线性相关性，发现局部片段能量的加和性质（负责氢键作用）是预测此类二聚体结合能的有效近似，并且发现该想法可扩展到这些酸/酰胺的其他同系物。
