Nonlinear optical response of sodium based superalkalis decorated graphdiyne surface: A DFT study

In the current study, structural, electronic, optical and nonlinear optical properties of superalkalis doped graphdiyne (GDY) complexes (Na₂Y@GDY, Y = SH, OCH₃, SCH₃, CN and N₃) are investigated. Our results show that superalkalis cluster preferably adsorb on the hollow cavity of GDY nanosheet. Na₂CN@GDY is thermodynamically stable among all considered complexes. NBO analysis reveals the transfer of charge from superalkalis to GDY is analyzed through. Doping of superalkalis on GDY significantly reduces the HOMO-LUMO gap of GDY. Na₂OCH₃@GDY complex has the lowest H-L gap (3.77 eV) with remarkable β_o (6.17 × 10⁴ au) value. The doping of GDY with superalkali introduces excess electrons into the system which significantly reduces the HOMO-LUMO gap by generating new HOMO orbitals. The involvement of superalkalis in diffusion of excess electrons towards GDY is confirmed through PDOS spectral analysis. Furthermore, the two-level model and first hyperpolarizability (β_vec) justified NLO properties of superalkalis doped GDY. According to the two-level model, the ΔE is the key factor for the enhancement of first hyperpolarizability values of all newly designed complexes.