The development of novel materials for vacuum electron sources in particle accelerators is an active field of research that can greatly benefit from the results of ab initio calculations for the characterization of the electronic structure of target systems. As state-of-the-art many-body perturbation theory calculations are too expensive for large-scale material screening, density functional theory offers the best compromise between accuracy and computational feasibility. The quality of the obtained results, however, crucially depends on the choice of the exchange–correlation potential, v _xc. To address this essential point, we systematically analyze the performance of three popular approximations of v _xc [PBE, strongly constrained and appropriately normed (SCAN), and HSE06] on the structural and electronic properties of bulk Cs₃Sb and Cs₂Te as representative materials of Cs-based semiconductors employed in photocathode applications. Among the adopted approximations, PBE shows expectedly the largest discrepancies from the target: the unit cell volume is overestimated compared to the experimental value, while the band gap is severely underestimated. On the other hand, both SCAN and HSE06 perform remarkably well in reproducing both structural and electronic properties. Spin–orbit coupling, which mainly impacts the valence region of both materials inducing a band splitting and, consequently, a band-gap reduction of the order of 0.2eV, is equally captured by all functionals. Our results indicate SCAN as the best trade-off between accuracy and computational costs, outperforming the considerably more expensive HSE06.

用于粒子加速器中真空电子源的新型材料的开发是一个活跃的研究领域，可以极大地受益于从头计算的结果来表征目标系统的电子结构。由于最先进的多体微扰理论计算对于大规模材料筛选来说过于昂贵，因此密度泛函理论在准确性和计算可行性之间提供了最佳折衷方案。然而，所获得结果的质量关键取决于交换相关势v _{xc 的选择}。为了解决这个关键点，我们系统地分析了v _xc的三种流行近似值的性能[PBE、强约束和适当规范 (SCAN) 和 HSE06] 关于块状 Cs ₃ Sb 和 Cs ₂的结构和电子特性Te 作为用于光电阴极应用的 Cs 基半导体的代表性材料。在采用的近似值中，PBE 与目标的预期差异最大：与实验值相比，晶胞体积被高估，而带隙被严重低估。另一方面，SCAN 和 HSE06 在再现结构和电子特性方面表现非常出色。自旋轨道耦合主要影响两种材料的价区，导致带分裂，因此带隙减少 0.2eV 量级，所有泛函都同样捕获。我们的结果表明 SCAN 是准确性和计算成本之间的最佳折衷方案，其性能优于昂贵得多的 HSE06。