U-Si systems have recently received considerable attention due to the potential application of U₃Si₂ as a high-density fuel under an accident tolerant fuel initiative. However, the thermodynamic stability of the more recently reported adjacent U₅Si₄ phase is uncertain and could play a significant role in fuel performance. In this work, the enthalpy of formation of the phase predicted by density functional theory (DFT) using the DFT + U formalism is used with an evolutionary algorithm (USPEX) to evaluate stability and possible atomic structures for U₅Si₄. The structure of U-Si convex hull phases and the confirmed U₃Si₂ structure were predicted providing confidence in the reliability of the evolutionary algorithm, as well as to obtain a convex hull with comparable enthalpies of formation. Subsequently, the code was applied to the U₅Si₄ composition for cells with 18 and 36 atoms, predicting a 36-atom hexagonal symmetrized unit cell with space group P6/mmm as the lowest-energy configuration, agreeing with that experimentally reported for U₅Si₄. Yet, phonon calculations using the density functional perturbation theory formalism, demonstrated that the predicted structure is dynamically unstable, exhibiting negative vibrational modes for the uranium. These indicated that generated shears are directed toward the formation of potential uranium octahedral sites, analogous to those occupied by carbon atoms in U₂₀Si₁₆C₃. It was thus concluded that omitting the U₅Si₄ phase from assessed U-Si phase equilibria is currently justified.

U-Si系统最近由于在事故容忍燃料计划下潜在地使用U ₃ Si ₂作为高密度燃料而受到了相当大的关注。但是，最近报道的相邻的U ₅ Si ₄相的热力学稳定性尚不确定，并且可能对燃料性能起重要作用。在这项工作中，使用密度泛函理论（DFT）使用DFT +  U形式主义预测的相的形成焓与进化算法（USPEX）一起使用，以评估U ₅ Si _4的稳定性和可能的​​原子结构。U-Si凸壳相的结构和确定的U ₃ Si ₂对结构进行了预测，从而为进化算法的可靠性提供了信心，并获得了具有可比的结构焓的凸壳。随后，将代码应用于具有18和36个原子的单元的U ₅ Si ₄组成，预测空间群为P6 / mmm的36原子六边形对称晶胞为最低能量构型，与实验报道的U构型一致₅硅₄。然而，使用密度泛函微扰理论形式主义进行的声子计算表明，所预测的结构是动态不稳定的，呈现出铀的负振动模式。这些表明所产生的剪切作用是指向潜在的铀八面体位点的形成，类似于U ₂₀ Si ₁₆ C _3中碳原子所占据的位置。因此得出的结论是，从评估的U-Si相平衡中删除U ₅ Si ₄相目前是合理的。