论文标题
具有机器学习电位的模拟确定了介导LGP中非Arrhenius行为的离子传导机制
Simulations with machine learning potentials identify the ion conduction mechanism mediating non-Arrhenius behavior in LGPS
论文作者
论文摘要
李$ _ {10} $ ge（ps $ _6 $）$ _ 2 $（LGPS）是一种高度浓缩的固体电解质，其中相邻阳离子之间的库仑拒绝被认为是concented离子跳的基本原因，在诸如li $ _7 $ la $ la $ zr $ _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 $ o _3 （llzo）和li $ _ {1.3} $ al $ _ {0.3} $ ti $ _ {1.7} $（po $ _4 $）$ _ 3 $（latp）。虽然使用分子动力学（MD）模拟的第一原理可以洞悉LI $^+$传输机制，但从历史上看，在模拟和实验中研究的温度范围存在差距。在这里，我们使用了经过密度功能理论（DFT）模拟训练的神经网络（NN）潜力，以在DFT样精度下运行高达40纳秒长的MD模拟，以表征包括先前模拟和实验性研究的一系列温度的离子传导机制。我们已经确认了LGPS中的Li $^+$ sublattice相过渡，在400 K左右，下面\ textit {ab} - 平面扩散率$ d^*_ {ab} $大大减少。伴随于400 K附近的Sublattice相变，阳离子丝（交叉）相关性较小，其特征是天堂比更接近1，并且系统中的振动在较低的温度下更为谐波。直观地，在高温下，振动模式的收集可能足以驱动协同的离子啤酒花。但是，近室温，可用的振动模式可能不足以克服静电排斥，从而导致相关的离子运动较少，离子传导较慢。 Sublattice相变的这种现象在下面，一致的跳跃起着不那么重要的作用，可以扩展到其他高度浓缩的固体电解质，例如LLZO和LATP。
Li$_{10}$Ge(PS$_6$)$_2$ (LGPS) is a highly concentrated solid electrolyte, in which Coulombic repulsion between neighboring cations is hypothesized as the underlying reason for concerted ion hopping, a mechanism common among superionic conductors such as Li$_7$La$_3$Zr$_2$O$_{12}$ (LLZO) and Li$_{1.3}$Al$_{0.3}$Ti$_{1.7}$(PO$_4$)$_3$ (LATP). While first principles simulations using molecular dynamics (MD) provide insight into the Li$^+$ transport mechanism, historically, there has been a gap in the temperature ranges studied in simulations and experiments. Here, we used a neural network (NN) potential trained on density functional theory (DFT) simulations, to run up to 40-nanosecond long MD simulations at DFT-like accuracy to characterize the ion conduction mechanisms across a range of temperatures that includes previous simulations and experimental studies. We have confirmed a Li$^+$ sublattice phase transition in LGPS around 400 K, below which the \textit{ab}-plane diffusivity $D^*_{ab}$ is drastically reduced. Concomitant with the sublattice phase transition near 400 K, there is less cation-cation (cross) correlation, as characterized by Haven ratios closer to 1, and the vibrations in the system are more harmonic at lower temperature. Intuitively, at high temperature, the collection of vibrational modes may be sufficient to drive concerted ion hops. However, near room temperature, the vibrational modes available may be insufficient to overcome electrostatic repulsion, thus resulting in less correlated ion motion and comparatively slower ion conduction. Such phenomena of a sublattice phase transition, below which concerted hopping plays a less significant role, may be extended to other highly concentrated solid electrolytes such as LLZO and LATP.
