Structure, Electronic Properties and Nonlinear Optical Properties of Silagraphdiyne (SiGDY): The Role of Alkali Metal Species

Novel graphdiyne (GDY) materials with tunable electronic and nonlinear optical (NLO) properties are always desirable for material development. Herein, we conducted a comprehensive prediction of silagraphdiyne (SiGDY) with the adsorption of alkali metals (M) and superalkalis molecules (M₂F) onto its surface, and their geometric structures, electronic properties, charge transfer and nonlinear optical responses were systematically studied. Our calculations demonstrate that the M/M₂F molecules can be adsorbed stably on large delocalized SiGDY surfaces reflected by high binding energies. Notably, the SiGDY can accept almost an electron transferred from M/M₂F, forming strong intramolecular charge-transfer (CT) process, while the reduced vertical ionization potentials (VIP) create the necessary conditions for enhancing the NLO response. Furthermore, it is found that both the substitution of silicon atoms within GDY and the adsorption of M/M₂F onto SiGDY significantly modulate electronic properties, and narrow the HOMO–LUMO gaps of complexes. More interestingly, the adsorption of M/M₂F on SiGDY enhances remarkably the first hyperpolarizability (β_tot) of complexes, especially for M@SiGDY, of which Li@SiGDY possesses the exceptionally large β_tot value (~7.65 × 10⁵ a.u.), further explained by two-level model. The present findings show that the functionalized SiGDY materials can be considered as promising candidate of novel carbon-based NLO nanodevices for future applications.