Wilkins David M, Manolopoulos David E, Dang Liem X
Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 93352, USA.
J Chem Phys. 2015 Feb 14;142(6):064509. doi: 10.1063/1.4907554.
We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell is found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the exchange processes are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium.
我们采用经典和环形聚合物分子动力学模拟来研究核量子涨落对锂离子和氟离子水溶液的结构及水交换动力学的影响。虽然通过用标准的 Lennard-Jones 离子-氧势增强离子与水分子之间的库仑相互作用，我们在锂离子溶液的模拟结果与实验数据之间取得了合理的良好一致性，但对于氟离子溶液却并非如此，我们发现具有较软排斥壁的势给出了更好的一致性。与经典模拟相比，在两种离子的量子模拟中都发现第一水合层有一定程度的不稳定，水合层变得不那么清晰，且水分子在该层中的平均停留时间减少。与这些适度差异一致的是，我们发现交换过程的机制不受量子化影响，因此对这些反应的经典描述给出了定性正确且定量合理的结果。我们还发现锂离子溶液中的量子效应比氟离子溶液中的更大。这部分是由于锂与水分子的相互作用更强，部分是由于锂的质量更轻，部分是由于氟离子水合过程中存在相互竞争的量子效应，而锂离子水合过程中不存在这种效应。
