Theoretical modification of C₂₄ fullerene with single and multiple alkaline earth metal atoms for their potential use as NLO materials

Density functional theory (DFT) calculations have been performed for the single and multi-alkaline earth metal atoms doped C₂₄ fullerene. All possible orientations have been optimized with different spin states to achieve the most stable geometry. Be₄@C₂₄ shows the highest interaction energy of −182.87 kcal mol⁻¹ among all complexes. The H-Lgap is increased in single doped complexes but is fairly reduced in all multi-doped cages, and the lowest H-Lgap is observed for Mg₄@C₂₄ (0.83 eV) which indicates the conductor behavior of this newly designed complex. NBO analysis is performed to confirm the charge transfer from metal toward the cage. The largest amount of charge (1.18 |e|) transfer has been observed for endohedral Mg@C₂₄ nanocage. Involvement of new HOMO orbitals (due to excess electrons) is confirmed from total density of states (TDOS) spectra of doped cages. It was observed that doping of alkaline earth metal atoms (Be, Mg and Ca) greatly enhanced the first hyperpolarizability. Among all these AEM_n@C₂₄ (AEM = Be, Mg and Ca, n = 1, 2, 3, 4) cages, Mg₄@C₂₄ shows the highest hyperpolarizability value of 3.62 × 10⁶ au with H-Lgap of 0.83 eV. The results of this study provide a guideline for the synthesis of highly efficient and thermodynamically stable nanocages for the optical and optoelectronic applications.