Duan Yuhua, Halley J W, Curtiss Larry, Redfern Paul
School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA.
J Chem Phys. 2005 Feb 1;122(5):54702. doi: 10.1063/1.1839555.
We report calculations using a previously reported model of lithium perchlorate in polyethylene oxide in order to understand the mechanism of lithium transport in these systems. Using an algorithm suggested by Voter, we find results for the diffusion rate which are quite close to experimental values. By analysis of the individual events in which large lithium motions occur during short times, we find that no single type of rearrangement of the lithium environment characterizes these events. We estimate the free energies of the lithium ion as a function of position during these events by calculation of potentials of mean force and thus derive an approximate map of the free energy as a function of lithium position during these events. The results are consistent with a Marcus-like picture in which the system slowly climbs a free energy barrier dominated by rearrangement of the polymer around the lithium ions, after which the lithium moves very quickly to a new position. Reducing the torsion forces in the model causes the diffusion rates to increase.
我们报告了使用先前报道的聚环氧乙烷中高氯酸锂模型进行的计算，以便了解锂在这些体系中的传输机制。使用由沃特尔提出的一种算法，我们得到的扩散速率结果与实验值相当接近。通过分析在短时间内锂发生大幅移动的个别事件，我们发现没有单一类型的锂环境重排能够表征这些事件。我们通过计算平均力势来估计这些事件中锂离子的自由能随位置的变化，从而得出这些事件中自由能随锂位置变化的近似图谱。结果与一种类似马库斯的图景一致，即体系缓慢地攀爬由锂离子周围聚合物重排主导的自由能垒，之后锂非常迅速地移动到一个新位置。降低模型中的扭转力会导致扩散速率增加。
