Optical spectra of 2D monolayers from time-dependent density functional theory

• Published in: Faraday discussions 2020-12, Vol.224, p.467-482
• Main Authors: Di Sabatino, S, Berger, J. A, Romaniello, P
• Format: Article
• Language: English
• Subjects: Condensed Matter; Density functional theory; Elementary excitations; Molybdenum disulfide; Monolayers; Physics; Spectra; Time dependence
• ISSN: 1359-6640; 1364-5498
• DOI: 10.1039/d0fd00073f

The optical spectra of two-dimensional (2D) periodic systems provide a challenge for time-dependent density-functional theory (TDDFT) because of the large excitonic effects in these materials. In this work we explore how accurately these spectra can be described within a pure Kohn-Sham time-dependent density-functional framework, i.e. , a framework in which no theory beyond Kohn-Sham density-functional theory, such as GW, is required to correct the Kohn-Sham gap. To achieve this goal we adapted a recent approach we developed for the optical spectra of 3D systems [S. Cavo, J. A. Berger and P. Romaniello, Phys. Rev. B , 2020, 101 , 115109] to those of 2D systems. Our approach relies on the link between the exchange-correlation kernel of TDDFT and the derivative discontinuity of ground-state density-functional theory, which guarantees a correct quasi-particle gap, and on a generalization of the polarization functional [J. A. Berger, Phys. Rev. Lett. , 2015, 115 , 137402], which describes the excitonic effects. We applied our approach to two prototypical 2D monolayers, h-BN and MoS 2 . We find that our protocol gives a qualitatively good description of the optical spectrum of h-BN, whereas improvements are needed for MoS 2 to describe the intensity of the excitonic peaks. Our recently developed pure Kohn-Sham approach for the calculation of optical spectra is applied to the challenging case of 2D monolayers. Our protocol yields a qualitatively good optical spectrum for h-BN, whereas improvements are needed for MoS 2 .