First-principles study of charge and magnetic ordering in monolayer NbSe2

Monolayer ${\mathrm{NbSe}}_{2}$ has recently been shown to be a two-dimensional superconductor, with a competing charge-density wave (CDW) order. This work investigates the electronic structure of monolayer ${\mathrm{NbSe}}_{2}$ based on first-principles calculations, focusing on charge and magnetic orders. It is found that decreased screening in the monolayer ${\mathrm{NbSe}}_{2}$ with a perfect lattice exhibits magnetic instability, which is removed by the formation of CDW. Two energetically competitive but distinct $3\ifmmode\times\else\texttimes\fi{}3$ CDW structures are revealed computationally, which have a significant impact on the Fermi surface. The relations of the potential CDW phases with experimental structure and the coexisting superconductivity are discussed.