Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, ${\mathrm{CeO}}_2$, at finite temperature. The results indicate that the previously proposed connection between the $B_{1u}$ phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the $E_u$ mode prevents the $B_{1u}$ mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

中文翻译：

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二氧化铈中的有限温度晶格动力学和超离子跃迁从第一原理开始

从头算分子动力学（AIMD）与温度相关有效电位（TDEP）方法相结合已被用于超越准谐波近似，并研究了二氧化铈的晶格动力学，${\mathrm{CEO}}_{\mathrm{2个}}$，在有限的温度下。结果表明，以前建议的连接之间${乙}_{\mathrm{1个}ü}$萤石结构材料中的声子模态虚构转变和超离子相转变是描述在高温下晶格动力学时准谐波近似失败的假象。相反，我们在TDEP图片中显示，声子模式耦合到$E_{ü}$ 模式可防止 ${乙}_{\mathrm{1个}ü}$从虚构的模式。我们在AIMD模拟中直接观察了高温下的超离子转变，发现它是由氧弗伦克尔对（FP）的形成引发的。发现这些FP是在涉及两个氧离子的同时运动的共同过程中形成的。