Accelerating <i>GW</i> Calculations of Point Defects with the Defect-Patched Screening Approximation

The GW approximation has been widely accepted as an ab initio tool for calculating defect levels with the many-electron effect included. However, the GW simulation cost increases dramatically with the system size, and unfortunately, large supercells are often required to model low-density defects that are experimentally relevant. In this work, we propose to accelerate GW calculations of point defects by reducing the simulation cost of many-electron screening, which is the primary computational bottleneck. The random-phase approximation of many-electron screening is divided into two parts: one is the intrinsic screening, calculated using a unit cell of pristine structures, and the other is the defect-induced screening, calculated using the supercell within a small energy window. Depending on specific defects, one may only need to consider the intrinsic screening or include the defect contribution. This approach avoids the summation of many conduction states of supercells and significantly reduces the simulation cost. We have applied it to calculate various point defects, including neutral and charged defects in two-dimensional and bulk systems with small or large bandgaps. The results are consistent with those from the direct GW simulations. This defect-patched screening approach not only clarifies the roles of defects in many-electron screening but also paves the way to fast screen defect structures/materials for novel applications, including single-photon sources, quantum qubits, and quantum sensors.GW近似（GW approximation）已被广泛认可为用于计算包含多电子效应的缺陷能级的从头算（ab initio）工具。然而，GW模拟的计算成本随体系规模急剧攀升，而实验相关的低密度缺陷往往需要借助大超胞进行建模，此二者间的矛盾尤为突出。在本研究中，我们提出通过降低作为核心计算瓶颈的多电子屏蔽的模拟成本，来加速点缺陷的GW计算。 多电子屏蔽的随机相位近似（random-phase approximation）可被拆分为两个部分：其一为本征屏蔽，通过本征结构的原胞进行计算；其二为缺陷诱导屏蔽，通过小能量窗口下的超胞完成计算。针对特定缺陷，研究者仅需考虑本征屏蔽，或仅引入缺陷贡献即可。该方法规避了对超胞大量导带态的求和操作，显著降低了模拟成本。 我们将该方法应用于多种点缺陷的计算，涵盖二维与块体体系中带隙大小各异的中性及带电缺陷。计算结果与直接GW模拟的结果保持高度一致。此缺陷补丁式屏蔽方法不仅阐明了缺陷在多电子屏蔽过程中的具体作用，更为面向新型应用的缺陷结构/材料的快速筛选铺平了道路，这些应用包括单光子源、量子比特以及量子传感器。