Department of Electronic and Nanostructured Materials, Sandia National Laboratories, Albuquerque, NM 87185, USA.
Phys Chem Chem Phys. 2011 Aug 14;13(30):13629-37. doi: 10.1039/c1cp20967a. Epub 2011 Jun 24.
Ab initio molecular dynamics (AIMD) simulations have been used to predict the time-averaged Li NMR chemical shielding for a Li(+) solution. These results are compared to NMR shielding calculations on smaller Li(+)(H(2)O)(n) clusters optimized in either the gas phase or with a polarizable continuum model (PCM) solvent. The trends introduced by the PCM solvent are described and compared to the time-averaged chemical shielding observed in the AIMD simulations where large explicit water clusters hydrating the Li(+) are employed. Different inner- and outer-coordination sphere contributions to the Li NMR shielding are evaluated and discussed. It is demonstrated an implicit PCM solvent is not sufficient to correctly model the Li shielding, and that explicit inner hydration sphere waters are required during the NMR calculations. It is also shown that for hydrated Li(+), the time averaged chemical shielding cannot be simply described by the population-weighted average of coordination environments containing different number of waters.
从头算分子动力学 (AIMD) 模拟已被用于预测 Li(+)溶液的时间平均 Li NMR 化学位移。这些结果与在气相或使用极化连续体模型 (PCM) 溶剂优化的更小的 Li(+)(H(2)O)(n)簇的 NMR 屏蔽计算进行了比较。描述了 PCM 溶剂引入的趋势，并与在 AIMD 模拟中观察到的时间平均化学位移进行了比较，在 AIMD 模拟中使用了大的显式水分子簇来水合 Li(+)。评估并讨论了对 Li NMR 屏蔽的内和外配位球的不同贡献。结果表明，隐式 PCM 溶剂不足以正确模拟 Li 屏蔽，并且在 NMR 计算期间需要显式的内水合球水。还表明，对于水合的 Li(+)，时间平均化学位移不能简单地用包含不同数量水的配位环境的加权平均来描述。
