Quasiparticle electronic structure of 1T'-MoS₂ within GW approximation

Two-dimensional transition metal dichalcogenides, such as MoS₂, exhibit several polymorphs, namely semiconducting 1H, metallic 1T, and semi-metallic 1T'. Recent experiment [Xinmao Yin et al., Nat. Commun. 8, 486 (2017)] showed an inverted gap of 0.5 eV and a fundamental gap of 0.1 eV in the absorption spectrum of the semi-metallic 1T'-MoS₂. We carry out first-principles calculations on the electronic band structure of 1T'-MoS₂. Since the transition across the fundamental gap occurs at a non-high-symmetry k-point, the choice of k-point sampling is crucial. Our converging result regarding k-point sampling shows that two bands touch at Fermi energy. It indicates the absence of fundamental gap. We report that spin-orbit interaction induces an opening of this fundamental gap of about 0.06 eV, which is smaller than the gap observed in experiment. To see the effects of electron-electron interaction on this fundamental gap, we calculate the quasiparticle electronic band structure within the GW approximation.