A Comparative Theoretical Study on Second‐Order Nonlinear Optical Properties of XAl 12 ‐Y (X = Be, Al, C, and P; Y = K and K 3 O )

ABSTRACT The electronic and nonlinear optical (NLO) properties of XAl 12 ‐Y (X = Be, Al, C, and P; Y = K and K 3 O) were systematically investigated theoretically. Density functional theory calculations demonstrated that the Y ligands bind strongly to the XAl 12 clusters with high binding energies. Natural population analysis revealed that an electron is transferred from (super)alkali to the XAl 12 cluster. XAl 12 ‐Y exhibits excellent NLO response, as evidenced by the calculated static and dynamic first hyperpolarizabilities, as well as hyper‐Rayleigh scattering (HRS) hyperpolarizabilities. The NLO responses critically depend on the XAl 12 core and ligand type, with PAl 2 ‐K, CAl 12 ‐K 3 O, and PAl 12 ‐K 3 O showing superior performance. The remarkable NLO responses of these systems primarily arise from (super)alkali ligands, underscoring the critical role of ligand introduction in enhancing the NLO response of the system. This work demonstrates that combining potent (super)alkalis with tunable superatom acceptors is a highly effective strategy for designing high‐performance NLO materials.