Constrained Density Functional Theory Molecular Dynamics Simulation of Deprotonation in Aqueous Silicic Acid
Constrained Density Functional Theory Molecular Dynamics Simulation of Deprotonation in Aqueous Silicic Acid
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约束密度泛函理论水硅酸中去质子化的分子动力学模拟
DOI：
10.1021/acs.jpcb.0c05096
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Ando Koji
中科院分区：
文献类型：
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作者：
Joutsuka Tatsuya;Ando Koji
硅酸在水中的溶解度如此之低，以至于人们对其物理性质背后的分子机制知之甚少，尽管它在化学和地质等领域具有重要意义。理论计算提供了关于这种稀有化学物种的分子水平的信息，但在选择反应坐标和凝聚相中质子转移(PTS)的罕见事件采样方面面临困难。我们提出了pKawith从头算分子动力学(MD)模拟和约束密度泛函理论(CDFT)的直接计算方案，提供了径向分布函数、振动光谱和反应路径等结构和动力学性质。在几千卡/摩尔范围内，计算的去质子化反应自由能与实验符合较好。对溶剂化结构的分析表明，去质子化后的氢离子D3O+与去质子化的硅酸SiO(OD)3-发生排斥反应，没有形成稳定的接触离子对。计算的振动光谱与光谱测量结果一致，反应路径的动力学分析根据包括溶质和溶剂组分的垂直能隙坐标，量化了硅酸和水的OD伸缩振动与PT反应的耦合。
The solubility of silicic acid in water is so low that the molecular mechanism behind the physical properties such as pKaremains poorly understood, despite the importance in fields such as chemistry and geology. Theoretical calculations provide the molecular-level information on such a rare chemical species yet face difficulties in the selection of reaction coordinates and the rare-event sampling of proton transfers (PTs) in condensed phases. We propose a straightforward calculation scheme of pKawithab initiomolecular dynamics (MD) simulation and the constrained density functional theory (CDFT), which provides structural and dynamical properties such as radial distribution functions, vibrational spectra, and reaction paths. The calculated reaction free energies of deprotonations agreed with experiments within a few kcal/mol. Analysis of the solvation structure shows that, after deprotonation, the hydronium ion D3O+repels away from the deprotonated silicic acid SiO(OD)3–without forming a stable contact-ion pair. The calculated vibrational spectra are consistent with the spectroscopic measurements, and the dynamical analysis of the reaction path quantifies the couplings of the OD stretch vibrations of silicic acid and water to the PT reaction in terms of the vertical energy-gap coordinate that includes both the solute and the solvent components.