Electronic and optical properties of crystalline nitrogen versus black phosphorus: A comparative first-principles study

TL;DR

This study compares the electronic and optical properties of crystalline black nitrogen and black phosphorus using advanced first-principles calculations, revealing significant differences in optical gaps, anisotropy, and mechanical stiffness.

Contribution

It provides the first systematic comparison of BN and BP's electronic, optical, and elastic properties using quasiparticle GW methods with vertex corrections.

Findings

BN has a larger optical gap than BP, making it transparent in visible light.

BN exhibits highly anisotropic optical responses due to reduced dielectric screening.

BN's elastic stiffness is comparable to diamond, indicating exceptional mechanical strength.

Abstract

Crystalline black nitrogen (BN) is an allotrope of nitrogen with the black phosphorus (BP) structure recently synthesized at high pressure by two independent research groups [Ji et al., Sci. Adv. 6, eaba9206 (2020); Laniel et al., Phys. Rev. Lett. 124, 216001 (2020)]. Here, we present a systematic study of the electronic and optical properties of BN focusing on its comparison with BP. To this end, we use the state-of-the-art quasiparticle self-consistent $GW$ approach with vertex corrections in both the electronic and optical channels. Despite many similarities, the properties of BN are found to be considerably different. Unlike BP, BN exhibits a larger optical gap (2.5 vs 0.26 eV), making BN transparent in the visible spectral region with a highly anisotropic optical response. This difference can be primarily attributed to a considerably reduced dielectric screening in BN, leading to enhancement of the effective Coulomb interaction. Despite relatively strong Coulomb interaction, exciton formation is largely suppressed in both materials. Our analysis of the elastic properties shows exceptionally high stiffness of BN, comparable to that of diamond.