Prediction of two-dimensional monochalcogenides: MoS and WS

Using density functional theory, we explore the possibility of two monolayer monochalcogenides, namely, MoS and WS. From the energetics, buckled and puckered structures are found to be more probable configurations. Our results on cohesive energy and phonon dispersion predict that the buckled structures of both MoS and WS are stable. On the other hand, while the puckered structure of WS clearly shows a dynamical instability, the same for MoS may have a stable configuration. Charge analyses predict ionic-like bonding in these systems. Density of states and band structure reveal a non-magnetic metallic nature for MoS in the stable configurations. However, for the buckled WS, our study predicts a non-magnetic semi-metallic nature. Further, semi-metal to indirect semiconductor transition has been observed for tensile strain of 5%, 6% and 8%.