Accelerating GW calculations of point defects with the defect-patched screening approximation

TL;DR

This paper introduces a fast GW calculation method for point defects that reduces computational costs by separating intrinsic and defect-induced screening, enabling efficient and accurate defect level predictions in large systems.

Contribution

The authors propose a defect-patched screening approximation that accelerates GW calculations by simplifying the many-electron screening process, especially for large supercells.

Findings

Accurately reproduces GW defect levels with reduced computational effort.

Effective for both 2D and bulk systems with various bandgaps.

Improves agreement with direct GW calculations at dilute defect limits.

Abstract

The GW approximation has been widely accepted as an ab initio tool for calculating defect levels with 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 the 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 conductions states of supercells and significantly reduces the simulation time. We have applied it to calculating various point defects, including neutral and charged defects in two-dimensional and bulk systems with small or large bandgaps. The results consist with those from the direct GW simulations, and the agreements are further improved at the dilute-defect limit, which is experimentally relevant but extremely challenging for 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.