水溶液中溶剂化氢氧化物和水合氢离子的结构和动力学性质的从头算研究
Structural and Dynamic Properties of Solvated Hydroxide and Hydronium Ions in Water from Ab Initio Modeling
摘要：
从从头计算分子动力学（AIMD）出发，预测水溶液中氢氧化物和水合氢离子的不对称结构和动力学是一项具有挑战性的任务。这一困难主要来自于缺乏准确有效的交换相关泛函来解释两种离子的两亲性和普遍存在的质子转移行为。通过采用强约束和适当赋范（SCAN）元GGA功能的AIMD模拟，我们系统地研究了两个水离子的两亲性，溶剂化结构，电子结构和动力学性质。特别是，我们将这些结果与PBE 0-TS泛函预测的结果进行了比较，PBE 0-TS泛函是一种精确但计算成本更高的交换相关泛函。我们证明，通用的扫描功能提供了一个可靠的选择，在描述两个水离子。具体而言，在水离子的SCAN图像中，第四和第五氢键的出现接近氢氧化物稳定的壶状形状的溶剂化结构和抑制结构扩散，而水合氢离子稳定地捐赠三个氢键给它的邻居。结果表明，氢氧化物倾向于逐步质子转移，而水合氢离子倾向于协同质子转移。因此，氢氧化物在水中的扩散比水合氢离子慢，这与实验一致。
英文摘要：
Predicting the asymmetric structure and dynamics of solvated hydroxide and hydronium in water has been a challenging task from ab initio molecular dynamics (AIMD). The difficulty mainly comes from a lack of accurate and efficient exchange-correlation functional in elucidating the amphiphilic nature and the ubiquitous proton transfer behaviors of the two ions. By adopting the strongly-constrained and appropriately normed (SCAN) meta-GGA functional in AIMD simulations, we systematically examine the amphiphilic properties, the solvation structures, the electronic structures, and the dynamic properties of the two water ions. In particular, we compare these results to those predicted by the PBE0-TS functional, which is an accurate yet computationally more expensive exchange-correlation functional. We demonstrate that the general-purpose SCAN functional provides a reliable choice in describing the two water ions. Specifically, in the SCAN picture of water ions, the appearance of the fourth and fifth hydrogen bonds near hydroxide stabilizes the pot-like shape solvation structure and suppresses the structural diffusion, while the hydronium stably donates three hydrogen bonds to its neighbors. As a result, hydroxide prefers the stepwise proton transfer (PT) while hydronium prefers the concerted PT behavior. Consequently, hydroxide diffuses slower than hydronium in water, which is consistent with the experiments.
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