Toward a Unified Picture of the Water Self-Ions at the Air鈥揥ater Interface: A Density Functional Theory Perspective
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- 作者：Marcel D. Baer ; I-Feng W. Kuo ; Douglas J. Tobias ; Christopher J. Mundy
- 刊名：Journal of Physical Chemistry B
- 出版年：2014
- 出版时间：July 17, 2014
- 年：2014
- 卷：118
- 期：28
- 页码：8364-8372
- 全文大小：406K
- ISSN：1520-5207
文摘
The propensities of the water self-ions, H3O+ and OH鈥?/sup>, for the air鈥搘ater interface have implications for interfacial acid鈥揵ase chemistry. Despite numerous experimental and computational studies, no consensus has been reached on the question of whether or not H3O+ and/or OH鈥?/sup> prefer to be at the water surface or in the bulk. Here we report a molecular dynamics simulation study of the bulk vs interfacial behavior of H3O+ and OH鈥?/sup> that employs forces derived from density functional theory with a generalized gradient approximation exchange-correlation functional (specifically, BLYP) and empirical dispersion corrections. We computed the potential of mean force (PMF) for H3O+ as a function of the position of the ion in the vicinity of an air鈥搘ater interface. The PMF suggests that H3O+ has equal propensity for the interface and the bulk. We compare the PMF for H3O+ to our previously computed PMF for OH鈥?/sup> adsorption, which contains a shallow minimum at the interface, and we explore how differences in solvation of each ion at the interface vs in the bulk are connected with interfacial propensity. We find that the solvation shell of H3O+ is only slightly dependent on its position in the water slab, while OH鈥?/sup> partially desolvates as it approaches the interface, and we examine how this difference in solvation behavior is manifested in the electronic structure and chemistry of the two ions.