Density functional theory (DFT) prediction of TMXSe Janus monolayers (TM = Cr, Mn, Ni; X = C, Si, Ge)

The vast chemical space of TMXSe (TM = Cr, Mn, Ni; X = C, Si, Ge) Janus monolayers was systematically investigated in both 1T and 1H phases using first-principles calculations to identify novel, stable 2D materials. Considering both 1T and 1H phases for each of the nine possible compositions, a total of eighteen monolayers were analyzed. While three have been previously reported, this work focuses on the remaining fifteen, evaluating their structural stability. A combined analysis of phonon dispersion, ab initio molecular dynamics, and elastic constants reveals that only CrCSe (1H) and CrGeSe (1T) are dynamically, thermally, and mechanically stable. Their calculated in-plane elastic constants C 11 are 78.9 and 98.3 N/m for CrCSe (1H) and CrGeSe (1T), respectively. These monolayers exhibit remarkably divergent properties. CrCSe (1H) is a semiconductor with a direct band gap of 0.24 eV and a highly polarized surface arising from significant charge transfer to carbon atoms.Bader analysis indicates a charge transfer of approximately 1.10 e from Cr, with 0.80 e transferred toward C. In contrast, CrGeSe (1T) is a metal with low net magnetization, approximately 0.35 μ B per unit cell at the PBE level, which remains finite ( 0.16 μ B ) upon inclusion of the Hubbard correction. The pronounced surface polarity of CrCSe and the metallic character with finite magnetization of CrGeSe suggest possible directions for further investigation in molecular adsorption and spin-dependent phenomena, respectively. However, additional adsorption and transport calculations are required to assess these potential applications. Our findings predict two new, stable 2D Janus monolayers with distinct electronic, magnetic, and surface properties, encouraging future experimental realization.