Magnetic ground state of monolayer CeI2: Occupation matrix control and DFT+ U calculations

The magnetic ground state is crucial for applications of two-dimension magnets because it determines the fundamental magnetic properties of the material, such as magnetic order, magnetic transition temperature, and low-energy excitation of the spin waves. However, simulations of the magnetism of local-electron systems are challenging due to the existence of metastable states. In this study, occupation matrix control and density functional theory plus Hubbard's U calculations are applied to investigate the magnetic ground state of monolayer CeI2. Following the predicted ferromagnetic (FM) order, the FM ground state and the FM metastable states are identified and found to have different values for the magnetic parameters. Based on the calculated magnetic parameters of the FM ground state, the Curie temperature is estimated to be 128 K for monolayer CeI2. When spin-orbit coupling (SOC) is considered, the FM ground state is further confirmed to contain both off-plane and in-plane components of magnetization. SOC is shown to be essential for reasonably describing not only magnetic anisotropy but also the local electronic orbital state of monolayer CeI2.