Structure, electronic, and nonlinear optical properties of superalkaline M₃O (M = Li, Na) doped cyclo18carbon

Cyclo18carbon has received considerable attention thanks to its novel geometric configuration and special electronic structure. Superalkalis have low ionization energy. Doping a superalkali in cyclo18carbon is an effective method to improve the optical properties of the system because considerable electron transfer occurs. In this paper, the geometry, bonding properties, electronic structure, absorption spectrum, and nonlinear optical (NLO) properties of superalkaline M₃O (M = Li, Na)-doped cyclo18carbon were studied by using density functional theory. M₃O and the C₁₈ rings are not coplanar. The C₁₈ ring still exhibits alternating long and short bonds. The charge transfer between M₃O and C₁₈ forms stable M₃O⁺C₁₈⁻ ionic complexes. C₁₈M₃O (M = Li, Na) shows striking optical nonlinearity, i.e., their first- and second-order hyperpolarizability (β_vec and γ_||) increase considerably at λ = 1907 nm and 1460 nm.