Role of charge transfer in the structure and dynamics of the hydrated proton.

Although it has long been recognized that multiple water molecules strongly associate with an extra proton in bulk water, some models and conceptual frameworks continue to utilize the classical hydronium ion (H3O+) as a fundamental building block. In this work, the nature of the hydronium ion in aqueous systems is examined using an ab initio energy decomposition analysis (EDA) that evaluates both the magnitude of and energetic stabilization due to charge transfer among H3O+ and the surrounding water molecules. The EDA is performed on structures extracted from dynamical bulk-phase simulations, and used to determine how frequently the pure hydronium ion, where the excess charge is primarily localized on H3O+, occurs under dynamic conditions. The answer is essentially never. The energetic stabilization of H3O+ due to charge delocalization to neighboring water molecules is found to be much larger (16 to 49 kcal/mol) than for other ions (even Li+) and to constitute a substantial portion (20% to 52%) of the complex's binding energy. The charge defect is also shown to have intrinsic dynamical asymmetry and to display dynamical signatures that can be related to features appearing in IR spectra.

尽管人们早就认识到在大量水中多个水分子与一个额外的质子紧密结合，但一些模型和概念框架仍然将经典的水合氢离子（H₃O⁺）作为基本构建单元。在这项工作中，利用从头算能量分解分析（EDA）研究了水体系中水合氢离子的性质，该分析评估了H₃O⁺与周围水分子之间电荷转移的程度以及由此产生的能量稳定化。EDA是对从动态体相模拟中提取的结构进行的，并用于确定在动态条件下纯的水合氢离子（即多余电荷主要集中在H₃O⁺上）出现的频率。答案基本上是从不。发现由于电荷离域到相邻水分子，H₃O⁺的能量稳定化（16到49千卡/摩尔）比其他离子（甚至Li⁺）大得多，并且占复合物结合能的很大一部分（20%到52%）。还表明电荷缺陷具有内在的动态不对称性，并显示出与红外光谱中出现的特征相关的动态特征。