Energetics and electronic structure of Janus WSSe formation by continuous chalcogen substitutions

Abstract We investigated the energetics and the electronic structure of Janus WSSe when formed by continuous sulfurization and selenization of WSe$_2$ and WS$_2$, respectively, using density functional theory combined with the effective screening medium method. The total energy of WS$_{2-x}$Se$_x$ is sensitive to the stoichiometry. The total energy increases monotonically as the substitutional surface selenization of WS$_2$ increases. The sulfurization of WSe$_2$ causes complex energetics with respect to the number of S atoms involved. Competition between the energy cost of polarization and the energy gain through S-W bond formation produces the compound WS$_{0.445}$Se$_{1.445}$, which is a metastable structure that gives the local minimum in the energy landscape. The electronic structures of the partially substituted structures are interpolated smoothly from those of Janus WS$_2$ and WSe$_2$.