Optical properties of bulk semiconductors and graphene/boron-nitride: The Bethe-Salpeter equation with derivative discontinuity-corrected DFT energies

TL;DR

This paper introduces an efficient implementation of the Bethe-Salpeter equation within GPAW, using GLLBSC functional energies to accurately predict optical properties and excitonic features of bulk and 2D materials, including graphene and h-BN.

Contribution

It combines the BSE with GLLBSC energies to improve computational efficiency and accuracy in predicting optical properties of semiconductors and 2D materials.

Findings

Excellent agreement with experimental dielectric functions and absorption onsets.

Accurate modeling of excitonic features in semiconductors and insulators.

Reduction of gaps in graphene/h-BN interface due to image charge screening.

Abstract

We present an efficient implementation of the Bethe-Salpeter equation (BSE) for optical properties of materials in the projector augmented wave method GPAW. Single-particle energies and wave functions are obtained from the GLLBSC functional which explicitly includes the derivative discontinuity, is computationally inexpensive, and yields excellent fundamental gaps. Electron-hole interactions are included through the BSE using the statically screened interaction evaluated in the random phase approximation. For a representative set of semiconductors and insulators we find excellent agreement with experiments for the dielectric functions, onset of absorption, and lowest excitonic features. For the two-dimensional systems of graphene and hexagonal boron-nitride (h-BN) we find good agreement with previous many-body calculations. For the graphene/h-BN interface, we find that the fundamental and optical gaps of the h-BN layer are reduced by 2.0 eV and 0.7 eV, respectively, compared to freestanding h-BN. This reduction is due to image charge screening which shows up in the GLLBSC calculation as a reduction (vanishing) of the derivative discontinuity.