This study investigates the structural and electronic properties of octahedral and hexagonal phases of CrX2 monolayers (where X = S, Se) using the Quantum ESPRESSO package. Employing a first-principles density functional theory (DFT) approach with generalized gradient approximation (GGA), we analyze the impact of lanthanide atoms (L = Ce, Pr, and Nd) on the structural and electronic features of CrX2. Total energy, bond length, bond angle, and curvature are examined both with and without lanthanide atoms. The primitive unit cell of the 2H/1T phase forms a 120° rhombus with space groups (P63/mmc)/(P31). Structural analysis demonstrates a direct correlation between atomic number and geometrical properties, where increasing lanthanide atomic number leads to longer Cr-X and L-X bond lengths, alongside the smaller X-Cr-X and X-L-X bond angles. A comparison of total energy between hexagonal and octahedral phases indicates that the latter exhibits greater stability. The band structure of CrX2 (where X = S, Se) monolayers is studied both with and without lanthanide atoms, concerning spin effects. The results show that the octahedral phase of CrX2 exhibits metallic behavior with multiple bands intersecting the Fermi level, while the hexagonal phase displays semiconducting behavior with band gap values of 0.30 eV and 0.44 eV, respectively. Concerning spin polarization in the presence of lanthanide atoms, CrX2 demonstrates half-metal behavior, suggesting its suitability for use in spintronic components.

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