Mixed superalkalis are a better choice than pure superalkalis for BN nanocages to design high-performance nonlinear optical materials.

Mixed superalkali clusters are a source of excess electrons, as their vertical ionization energies (2.81-3.36 eV) are much lower than those of alkali metals (even cesium (∼3.85 eV)) and the superalkali LiO (3.42 eV). In the present work, the geometric, electronic, and nonlinear optical (NLO) properties of mixed superalkali cluster-doped BN nanocages are studied theoretically. All complexes, A-G, have very high interaction energies (-98.02 to -123.13 kcal mol) and are thermodynamically stable when compared to previously reported LiO@BN (-92.71 kcal mol). The designed complexes have smaller HOMO-LUMO energy gaps (3.36-4.27 eV) than pristine BN (11.13 eV). Charge transfer in the complexes is studied through natural population analysis and non-bonding interactions are evaluated through quantum theory of atoms in molecules (QTAIM) and non-covalent interaction analyses. These complexes have absorption maxima (1076-1486 nm) in the near-infrared region (NIR) and they are transparent in the UV region. The first hyperpolarizability of complex C is 1.7 × 10 au, which is much higher than the value of 3.7 × 10 au for a pure LiO superalkali-doped BN complex calculated at the same level of theory, as reported by Sun (, 2016, , 7500-7509). The large second hyperpolarizability values also reflect the enhanced nonlinear optical response. The best computed values for the electro-optical Pockels effect, second harmonic generation, and hyper-Rayleigh scattering are 3.29 × 10 au, 1.17 × 10 au, and 6.71 × 10 au, respectively. Furthermore, the electro-optic dc-Kerr effect and electric-field-induced second harmonic generation have maximum values of 3.96 × 10 au and 3.46 × 10 au at 1064 nm. There are enhancements in the quadratic nonlinear refractive index () values for complexes A-G, with a highest value of 3.35 × 10 cm W at 1064 nm. These results suggest that mixed-superalkali-doped BN nanoclusters are potential candidates when designing high-performance NLO materials.