Lithiated Graphene Quantum Dot and its Nonlinear Optical Properties Modulated by a Single Alkali Atom: A Theoretical Perspective

The functional modification in graphene leads to novel characteristics. We study a lithiated graphene quantum dot (LiG) and adsorption of a single alkali atom (M = Li, Na, and K) on its surface using the B3LYP-D3 method. The structures of M@ LiG attain the lowest energy with M adsorbed on the terminal ring of LiG. The isomers of M@LiG are stable against dissociation into M and LiG. The frontier orbital energy gap of M@LiG is significantly reduced to 0.41-0.58 eV as compared to that of LiG (2.16 eV). There is a strong charge transfer of 0.91-0.961e1 from M to LiG in all M@LiG systems, which is slightly reduced in the lowest-energy Na@LiG structure. The CAM-B3LYP results suggest a significant increase in the dipole moment and mean polarizabilities of M@LiG due to the charge transfer and smaller energy gaps, respectively. The first static hyperpolarizability (beta(0)) value of the lowest-energy M@LiG structures becomes as large as 11.5 x 10(5) a.u. for M = K. Our time-dependent density functional theory (TDDFT) calculations suggest that the enormously high value of beta(0) results due to lower transition energy and higher transition dipole moment for the crucial electronic transition.

Automated summary

The study shows that alkali metal atoms adsorbed on the surface of LiG can significantly reduce the energy gap of M@LiG structure, leading to strong charge transfer, increased dipole moment, and polarizabilities. The lowest-energy M@LiG structures exhibit extremely high static hyperpolarizability values.