Microscopic screening theory for excitons in two-dimensional materials: A bridge between effective models and ab initio descriptions

TL;DR

This paper introduces a quantum-screened, atomistic computational method for exciton calculations in 2D materials that improves accuracy over classical models while maintaining manageable computational costs.

Contribution

It develops a novel approach that explicitly computes dielectric screening at the RPA level, bridging effective models and ab initio methods for exciton calculations in 2D materials.

Findings

Captures screening effects beyond classical models with first-principles accuracy

Provides realistic estimates of excitonic binding energies

Highlights convergence issues affecting binding energy dispersion

Abstract

We present a computational approach for exciton calculations in two-dimensional (2D) materials within the Bethe-Salpeter equation (BSE) framework, employing an atomistic description with point-like orbitals. Unlike widespread efficient calculations that rely on classical or effective interaction models, such as the Rytova-Keldysh model, our method incorporates quantum screened interactions. By explicitly computing the 2D dielectric function at the random-phase approximation level, we capture screening effects beyond such approximations with an accuracy akin to first-principles methods. Consequently, we can realistically estimate excitonic binding energies with a bearable computational cost. A detailed account of the various convergence parameters sheds light on a possible cause of the large dispersion of binding energies reported in the literature using first-principles GW/BSE implementations. This work thus provides an alternative pathway towards efficient and faithful dielectric screening and exciton computations in low-dimensional materials.