Ultra-Large Nonlinear Optical Properties of Boron and Nitrogen Co-Doped Graphdiyne: The Role of the Alkalides

The structural, electronic and nonlinear optical (NLO) properties of BN-substituted graphdiyne (BNGDY) with the doping of Li3NM (M = Li, Na, and K) alkalides are systematically studied using density-functional theory calculations, in order to disclose the effect of the alkalides on molecular optical properties. The results show that the Li3NM alkalides can stably adsorb on the surface of six planar BNGDY structures, of which the structures with small substitution ratios of BN-pairs on diacetylenic linkages exhibit strong chemical stabilities. Moreover, the Li3NM alkalides have the slightly increased charge transfer with alkali metals from Li to K, and that is a decreasing trend with increasing BN substitution ratios (A → F) on GDY. More interestingly, the successive introduction of the alkalides on BN-substituted graphdiyne can effectively modulate the electronic properties and nonlinear optical responses of the systems. Importantly, the BNGDY structure (D) with the doping of Li3NLi on triangular hole possesses the excellent nonlinear optical performance with much larger first hyperpolarizability values (e.g., 1.890 × 106 a.u.), which can be further understood by the analysis of the first hyperpolarizability density and the two-level model from the excitation energy calculations. This study will inevitably provide an excellent strategy for designing the next generation high-performance NLO materials.