Enormously Large Nonlinear Optical Properties of Li ₂ F@Si ₆₀ ‐LiF ₂ : A First Principle Study

Abstract

ABSTRACT In this paper, we propose a new class of NLO active complex Li 2 F@Si 60 ‐LiF 2 composed of encapsulated superalkali Li 2 F and doped superhalogen LiF 2 with Si 60 , using a combination of the DFT/B3LYP method and the 6–31G (d) basis set. The optimized Si 60 structure is compared to Li 2 F@Si 60 ‐LiF 2 . The reactive index of Li 2 F@Si 60 ‐LiF 2 differs from that of Si 60 , as determined by frontier molecular orbitals. Charge transfer from a donor to an acceptor species results in the formation of a nonlinear optical (NLO)‐ active complex. The electron transfer index (ECT) demonstrates that charge transfer from Si 60 @Li 2 F to superhalogen alkali (LiF 2 ) occurs during the formation of the Li 2 F@Si 60 ‐LiF 2 complex. The DOS plot demonstrates that the additional unoccupied energy levels introduced by Li 2 F@Si 60 ‐LiF 2 resulted in a reduced energy gap compared to Si 60 , causing both the HOMO and LUMO energy levels to shift to the upper side. More polarization results due to the decreased frontier orbital energy gap. Li 2 F@Si 60 ‐LiF 2 ’s nonlinear optical behavior is computed using the dipole moment, polarizability, and hyperpolarizability, and compared to the Si 60 cage's corresponding properties. The moment of π electron caused a considerable boost in hyperpolarizability (4452.275 a.u.) in the interaction between superhalogen LiF 2 and encapsulated Si 60 with Li 2 F. The nonlinear‐optical characteristics of a single‐molecule gas phase of Li 2 F@Si 60 ‐LiF 2 have been explored, disregarding all effects in other solvents.