A Comparative Theoretical Study on Second-Order Nonlinear Optical Properties of XAl12-Y (X = Be, Al, C, and P; Y = K and K3O)

Abstract

The electronic and nonlinear optical (NLO) properties of XAl₁₂-Y (X = Be, Al, C, and P; Y = K and K₃O) were systematically investigated theoretically. Density functional theory calculations demonstrated that the Y ligands bind strongly to the XAl₁₂ clusters with high binding energies. Natural population analysis revealed that an electron is transferred from (super)alkali to the XAl₁₂ cluster. XAl₁₂-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 XAl₁₂ core and ligand type, with PAl₂-K, CAl₁₂-K₃O, and PAl₁₂-K₃O 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.