DFT study of super-halogen (Al7) doped carbon nitride (C2N) and its nonlinear optical properties

In this study, density functional theory (DFT) has been employed to conduct a systematic study of a non-linear optical and electrical characteristic of a specific class of carbon nitride (C2N) doped with super-halogen cluster (Al7). The optimization of molecular geometries of pure C2N (A1), single doped Al7@C2N (A2), and double doped 2Al7@C2N (A3) systems and comparison of their NLO properties are carried out at three functionals CAM-B3LYP, B3LYP, and LC-BLYP along with 6-31G basis set. Among these three methods of DFT, the B3LYP method provides the lowest bandgap and highest first hyperpolarizability (βo). The doping of Al7 on C2N significantly enhances the charge transfer characteristics by lowering the bandgap (Eg) from 2.32 eV to 0.99 and 0.95 eV for A1, A2, and A3 systems respectively. βo and dipole moment (μ) also increase remarkably from 1649 to 30221 au and 2.04 to 10.26 D, respectively. Among all the three A1, A2, and A3 systems, A2 system is extraordinarily efficient in HOMO and LUMO energies, Eint, EVI, as well as UV-Vis absorption. A2 exhibits significant absorption in the far-red region, which has been utilized in lasers. TD-DFT calculations along with FMO, DOS, and EDDM analysis were utilized to track down the source of electro-optical and structural property correlations. The mentioned systems, particularly single doped A2 system, have the opportunity to be used as useful NLO material.