Estimation of the single-particle band gap and exciton binding energy in two dimensional insulators: a modified G0W0-BSE method approach

In this paper we present an alternative G(0)W(0)-BSE procedure, suitable for calculation of the quasi-particle and optical properties in 2D semiconductors. The method completely excludes the spurious Coulomb interaction with 2D crystal replicas. The calculated band gap energies of hexagonal boron nitride (hBN), MoS(2)and MoTe(2)monolayers are in good agreement with other theoretical results. The 2D Bethe-Salpeter equation is derived and reduced to a 2D-hydrogen Schrodinger equation in which enter the G(0)W(0)band gap, DFT effective masses, and RPA screened Coulomb interaction. This formulation is applied to the problems of determining exciton binding energies and estimating the quasiparticle band gap in hBN, as well as in some transition-metal dichalcogenides. A semiclassical procedure is used in the limit of high polarizability lambda in order to obtain the analytical expression for exciton binding energies.