超薄二维材料带电缺陷电离能计算的基本原理
Fundamental Principles for Calculating Charged Defect Ionization Energies in Ultrathin Two-Dimensional Materials
摘要：
二维材料中的缺陷正成为量子发射器和可扩展光电应用的突出候选者。然而，表征其行为的几个物理性质，如带电缺陷电离能，很难用传统的第一原理方法模拟，主要是因为由降维引起的弱和各向异性介电屏蔽。我们建立的基本原则，准确和有效的计算带电缺陷电离能和电子结构的二维材料。我们建议使用真空水平作为参考缺陷电荷跃迁能级（CTL），因为它给出了强大的结果不敏感的理论水平，不像常用的带边位置。此外，我们确定的分数Fock交换混合泛函准确的带隙和带边位置的二维材料通过执行广义Koopmans的条件的局域缺陷状态。我们发现所得到的Fock交换分数从本体$h$ -BN的0.2变化到单层$h$ -BN的0.4，其带隙也与实验结果和计算的GW结果吻合得很好。这些方法的组合允许可靠且有效地预测缺陷电离能（CTL与带边缘位置之间的差异）。我们用几个例子来激发和概括这些发现，包括单层到少层六方氮化硼（$h$），单层MoS $_2$和石墨烷中的不同缺陷。最后，我们发现，增加层数的$h$ -BN系统地降低缺陷电离能，主要是通过CTL向真空移动，与导带极小值几乎保持不变。
英文摘要：
Defects in 2D materials are becoming prominent candidates for quantum emitters and scalable optoelectronic applications. However, several physical properties that characterize their behavior, such as charged defect ionization energies, are difficult to simulate with conventional first-principles methods, mainly because of the weak and anisotropic dielectric screening caused by the reduced dimensionality. We establish fundamental principles for accurate and efficient calculations of charged defect ionization energies and electronic structure in ultrathin 2D materials. We propose to use the vacuum level as the reference for defect charge transition levels (CTLs) because it gives robust results insensitive to the level of theory, unlike commonly used band edge positions. Furthermore, we determine the fraction of Fock exchange in hybrid functionals for accurate band gaps and band edge positions of 2D materials by enforcing the generalized Koopmans' condition of localized defect states. We found the obtained fractions of Fock exchange vary significantly from 0.2 for bulk $h$-BN to 0.4 for monolayer $h$-BN, whose band gaps are also in good agreement with experimental results and calculated GW results. The combination of these methods allows for reliable and efficient prediction of defect ionization energies (difference between CTLs and band edge positions). We motivate and generalize these findings with several examples including different defects in monolayer to few-layer hexagonal boron nitride ($h$-BN), monolayer MoS$_2$ and graphane. Finally, we show that increasing the number of layers of $h$-BN systematically lowers defect ionization energies, mainly through CTLs shifting towards vacuum, with conduction band minima kept almost unchanged.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
