Grupo de Física-Matemática da Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal.
J Phys Chem B. 2009 Dec 17;113(50):16151-8. doi: 10.1021/jp904901b.
The hydration of Na(+) in a water cluster is studied through all-electron Born-Oppenheimer molecular dynamics. The structure, dipole moment, and vibrational spectrum of the sodium cation hydration shells are examined. Emphasis is placed on the extent of the effect of the hydrated cation on the cluster properties. Our results show that hydration of Na(+) takes place in the interior of the cluster leading to significant changes in the hydrogen-bond (H-bond) network beyond the first hydration shell. In particular, we find that single acceptor-only H-bond arrangements increase significantly at the surface of the cluster relative to a neat water cluster. The vibrational spectrum of the first hydration shell of the cation, comprised mostly of H-bond double donor-single acceptor water molecules, is similar to that found for water molecules in the interior of a neat water cluster, although a small blue shift of the OH stretching band is observed. Further, a small reduction of the dipole moment of water molecules in the first hydration shell of the cation relative to a neat water cluster is also observed, and this persists to a minor extent when we move from the interior to the surface of the cluster. The present results indicate that the effect of the Na(+) on the cluster properties, although not pronounced, is not constrained to the first hydration shell. The reason appears to lie mostly in the specific orientation of the water molecules in the first coordination sphere, inducing modifications on the H-bond network topology of the cluster.
通过全电子 Born-Oppenheimer 分子动力学研究了 Na(+)在水团簇中的水合作用。考察了钠离子水合壳层的结构、偶极矩和振动光谱。重点研究了水合阳离子对团簇性质的影响程度。我们的结果表明，Na(+)的水合作用发生在团簇内部，导致超出第一水合壳层的氢键（H-bond）网络发生显著变化。特别是，我们发现与纯净水团簇相比，在团簇表面单受体-only H-bond 排列显著增加。阳离子第一水合壳层的振动光谱主要由 H-bond 双供体-单受体水分子组成，与纯净水中水分子的振动光谱相似，尽管观察到 OH 伸缩带的小蓝移。此外，还观察到阳离子第一水合壳层中水分子的偶极矩相对于纯净水团簇略有减小，当我们从团簇内部移动到表面时，这种减小程度略有减小。目前的结果表明，Na(+)对团簇性质的影响虽然不明显，但不限于第一水合壳层。原因似乎主要在于第一配体球中水分子的特定取向，诱导了团簇氢键网络拓扑的修改。
