Structural, electronic, and energetic modifications in alkali metal-doped Ge₁₂C₁₂ nanocages for tuning nonlinear optical response, energetic offsets, and charge transfer dynamics: computational insights for advanced photonic materials

The development of next-generation optoelectronic and photonic devices requires advanced materials with superior nonlinear optical (NLO) properties. Despite significant efforts, the design of stable, efficient, and tunable NLO materials at the nanoscale remains a key challenge. In this context, exploring novel materials with extraordinarily large NLO responses is an intriguing field of study. Density functional theory (DFT) calculations were carried out for exohedral alkali metal-doped Ge₁₂C₁₂ nanocage in order to examine their geometric, electronic, and nonlinear optical properties. Interaction energy (E_int) computations were employed to study the thermal stability of the complexes under consideration, with the highest interaction energy being − 50.72 kcal/mol. After doping with Li, Na, and K, the E_HL gap decreased, with the lowest E_HL gap being measured at 1.66 eV for Na@r₄-GeC. The TD-DFT computations illustrate that the complexes of Ge₁₂C₁₂ are transparent in the UV region. The natural bond orbital (NBO) and total density of state (TDOS) and partial density of state (PDOS) studies were used to investigate the participation of various segments and confirm charge transfer, respectively. The type of interaction was examined through IRI and QTAIM analyses, which assured the existence of non-covalent interactions between alkali metals and nanocages. The complex of Na@r₄ displays a first hyperpolarizability value of 3.4 × 10⁴ au. Therefore, the results demonstrate that the doped complexes of Ge₁₂C₁₂ nanocage with alkali metals are promising candidates for nanoscale materials because of their enhanced NLO responsiveness and excellent stability. This study addresses the rational design strategy for creating high NLO response materials for novel optoelectronic applications.