DFT study of Benzene, Coronene and Circumcoronene as zigzag graphene quantum dots

Theoretically, graphene quantum dot (GQD) has proved to feature in several important applications during recent decades. Generally, quantum dot, which is of nano-scale size is comparable to the size of atoms and molecules, having different properties from the bulk of the same materials. In Nano scales, the electrical, optical, thermodynamic, and mechanical properties of samples are directly related to the number of atoms constituting the sample, regarding size and shape (type of edge, forms, and dimensions). In this paper three different structures of GQDs with zigzag edges (Benzene, Coronene, and Circumcoronene) have been considered and simulated using the DFT theory by applying PBE functional in order to extract the thermal energy, electronic energy, heat capacity, polarizability, and entropy of each structure. The modification of each property with respect to the number of atoms in the GQD are investigated, linear and nonlinear variations of these properties with respect to the atom number are observed. Comparative study of Raman spectroscopy between PBE and B3LYP functionals is studied for each size of the considered GQDs. Also, revolution of the G peak in each case has been separately investigated. All calculations are done by using the Gaussian 09W software package based on 3-21G Gaussian basis sets.