First Principles Investigation of Rare Earth Decorated Benzene Complexes

Rare-earth benzene (RE(Bz)) complexes have garnered attention for their roles as catalysts in polymerization and hydrogenation reactions, as well as for their optical properties. Using first-principles density functional theory (DFT), the geometries, stability, and electronic, magnetic, optical, and nonlinear optical properties of RE(Bz) complexes (RE = La–Lu) were investigated. The results show that complexes with lower spin multiplicities stabilize in lower-symmetry structures (C_2v and C₂) due to Jahn–Teller distortions. Metastable states were observed for the Er(Bz) and Tm(Bz) complexes. Natural population analysis showed a dominant 6s → 5d electron transition in most of the complexes. Optical absorption results reveal that benzene allows forbidden d–d transitions in RE elements. Magnetic moments exhibit spin enhancement from Pr(Bz) to Gd(Bz) and from Ho(Bz) to Tm(Bz), while spin quenching occurs in the Dy(Bz) complex. Nonlinear optical properties show distinct trends in polarizability(α₀), first hyperpolarizability(β₀), and second hyperpolarizability(γ₀) across the lanthanide series.