First-principles modeling of 3d-transition-metal-atom adsorption on silicene: A linear-response DFT + U approach

By employing DFT + U calculations with the linear response method, we investigate the interactions between various 3d transition-metal atoms (Cr, Mn, Fe, Co) and silicene. In the cases of two-dimensional (2D) FeSi₂ and CoSi₂, the metal atoms tend to penetrate into the silicene layer. While CoSi₂ is non-magnetic, FeSi₂ exhibits a total magnetic moment of 2.21 μ _B/cell. Upon the examination of 2D MSi₆, a trend in anti-ferromagnetic (AFM) favorability in the z-direction is observed according to our DFT + U calculations. In the ferromagnetic (FM) states (less stable), each primary unit cell of CrSi₆, MnSi₆, and FeSi₆ possesses different levels of total magnetization (4.01, 5.18, and 2.00 μ _B/cell, respectively). The absolute magnetization given by AFM MSi₆ structures varies in the range of 5.33-5.84 μ _B/cell. A direct band gap in AFM MnSi₆ (0.2 eV) is predicted, while the metastable FM FeSi₆ structure has a wider band gap (0.85 eV). Interestingly, there are superexchange interactions between metal atoms in the MSi₆ systems, which result in the AFM alignments.