While the electronic stoppage of charged fission fragments is relatively well understood, the subsequent energy cascade is not. Recent efforts to investigate this cascade and predict the resulting damage have used a two-temperature model (TTM) of the electronic and phononic systems coupled with a classical molecular dynamics (MD) simulation of the crystal lattice. In order to accurately predict the track radius produced by a fission fragment in UO₂, this model (TTM + MD) requires that UO₂, an insulator, have metallic properties, e.g., a substantial electron thermal conductivity and heat capacity. However, it has been predicted that UO₂ becomes metallic under large pressures, and we perform ab initio (DFT-HSE) simulations to support this prediction. We show that the average U-U bond length decreases within and near the ion track during TTM + MD simulations, supporting the use of volume contraction to model the pressurized UO₂ cell. Additionally, we evaluate the electron, phonon, and electron-phonon coupling properties of UO₂ for variations in the pressure. In particular, we calculate the electronic heat capacity and thermal conductivity, and the electron-phonon energy coupling for use in subsequent TTM + MD simulations. The ab initio parameterized TTM + MD simulations provide a set of the track radii predictions which bracket and include the experimentally observed radii. The accuracy of the ab initio parameterized TTM + MD simulations depends on the pressure and degree of electron-phonon non-equilibrium assumed during the ab initio calculations. We suggest improvements to the current TTM + MD methodology in light of these results. Still, we show that the pressure-induced transition of UO₂ from insulator to metal and subsequent energy transfer from the electronic to phononic systems can accurately explain radiation damage during swift, heavy ion stoppage in UO₂. We make some additional observations regarding the accumulation and recombination of damage along the ion track and make comparison to the common SRIM model of ion stoppage and damage accumulation.

尽管对带电裂变碎片的电子停止的理解相对较好，但随后的能量级联却没有。最近研究这种级联并预测所造成的损害的努力已经使用了电子和声子系统的双温度模型（TTM），并结合了晶格的经典分子动力学（MD）模拟。为了准确地预测UO _2中裂变碎片产生的轨道半径，此模型（TTM + MD）要求绝缘体UO ₂具有金属特性，例如，很大的电子热导率和热容。但是，据预测，UO ₂在大压力下会变成金属，并且我们会从头开始（DFT-HSE）模拟以支持此预测。我们显示，在TTM + MD模拟过程中，平均UU键长度在离子轨道内和离子轨道附近减小，从而支持使用体积收缩对加压的UO ₂电池进行建模。此外，我们评估了UO ₂的电子，声子和电子-声子耦合特性对压力变化的影响。特别是，我们计算电子热容和热导率，以及电子声子能量耦合，以用于后续的TTM + MD仿真。在从头参数TTM + MD模拟提供一组轨道半径的预测，其支架以及包括实验观察到的半径。从头算起的准确性参数化的TTM + MD模拟取决于从头算计算中假设的电子声子不平衡的压力和程度。根据这些结果，我们建议对当前的TTM + MD方法进行改进。仍然，我们证明了压力引起的UO ₂从绝缘体到金属的转变以及随后从电子系统到声子系统的能量转移可以准确地解释UO ₂迅速，严重的离子停止过程中的辐射损伤。我们对沿离子径迹的损伤的积累和复合进行了其他观察，并与离子停止和损伤积累的普通SRIM模型进行了比较。