Optical spectrum and excitons in bulk and monolayer MX₂ (M=Zr, Hf; X=S, Se)

Abstractauthoren We present first principles calculations of the electronic and optical properties of bulk and monolayer structures for four transition metal chalcogenides, MXMZr and Hf; XS, Se), using a post density functional many-body perturbation GW approximation in conjunction with the Bethe–Selpeter approximation (GW-BSE). Optical absorption spectra predict the presence of a strongly bound exciton that lies below the direct band gap in two bulk (HfS and ZrSe) and in all the monolayer structures. The binding energy of the excitons are predicted to lie between 0.11 and 0.96 eV.