Effects of lithium impurities on electronic and optical properties of graphene nanoflakes: A DFT-TDDFT study

Using the density function theory (DFT) and time-dependent density function theory (TD-DFT) methods, we investigated the electronic and optical properties of lithium (Li) impurity doped-graphene nanoflakes (GNFs). It is observed that GNFs structure in a pure state exhibiting semiconductor behavior with big bandgap. Depending on structural properties of Li impurity in GNFs structure, the electronic properties at the ground and low-lying excited states of the structures may vary. As a result of calculations, it has been determined that Li impurity affects the bandgap values of GNFs structure significantly. The results show that the electronic properties of GNFs depend on the geometrical pattern of Li impurity in the GNFs structure. The bandgap of GNFs is hardly red-shifted by the doping of Li impurity due to the interaction with the sp-hybrid orbital. The effects of Li impurity both the ground and excited electronic states of GNFs were discussed. In addition, we can provide bandgap tuning of GNFs by doping Li as required, and for its application in solar cell and nanoelectronic devices.