Identifying the Ground State Geometry of a MoN₂ Sheet through a Global Structure Search and Its Tunable p-Electron Half-Metallicity

MoN 2 and MoS 2 sheets are representatives of two-dimensional transition metal dinitrides and dichalcogenides, respectively. Their similarity in atomic ratios misled people to make an incorrect assumption in previous studies that the former adopts the geometry of the latter. However, compared with S, N is smaller and has fewer valence electrons, and N is more effective in mediating magnetic couplings; therefore, a different geometry and different properties can be expected for the MoN 2 sheet. Here using a global structure search, for the first time we have identified the ground state geometry of this sheet named Tetra-MoN 2 that is much more stable than the H phase proposed previously. Different from the metallic nature of H-MoN 2, Tetra-MoN 2 is a semiconductor having an indirect band gap of 1.41 eV with a flexible strain tunability. In particular, Tetra-MoN 2 can exhibit rich half-metallic behaviors mediated by the polarized p electron of N and induced by low-concentration hole doping and small strains that are readily achievable experimentally.