Band structure and excitonic properties of monolayer WSe₂ in an all-electron QSGW^ approach

In this work we study the electronic band structure and optical absorption spectrum of monolayer WSe₂ using an all-electron quasiparticle self-consistent GW approach, QSGW^, in which the screened Coulomb interaction W^ is calculated by including ladder diagrams representing electron-hole interactions. We employ the Bethe-Salpeter equation to calculate the screened Coulomb interaction W^ both in the quasiparticle band structure and in the macroscopic dielectric function. The convergence of the quasiparticle band gap and lowest optical peak position is studied as a function of the spatial separation of the monolayers when using periodic boundary conditions. The quasiparticle gap is found to scale with 1/L where L is the size of the vacuum separation, while the lowest peak reaches convergence much faster. In addition, the Bethe-Salpeter equation provides us with information on the excitonic spectrum. We focus on the first few excitonic states, determining their brightness and further analyzing their wave vectors projected onto momentum and real space, and compare them to the hydrogenic model.