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

Theoretically, graphene quantum dot (GQD) has proved to feature in severalimportant applications during recent decades. Generally, quantum dot, which isof nano-scale size is comparable to the size of atoms and molecules, havingdifferent properties from the bulk of the same materials. In Nano scales, theelectrical, optical, thermodynamic, and mechanical properties of samples aredirectly related to the number of atoms constituting the sample, regarding sizeand shape (type of edge, forms, and dimensions). In this paper three differentstructures of GQDs with zigzag edges (Benzene, Coronene, andCircumcoronene) have been considered and simulated using the DFT theory byapplying PBE functional in order to extract the thermal energy, electronicenergy, heat capacity, polarizability, and entropy of each structure. Themodification of each property with respect to the number of atoms in the GQDare investigated, linear and nonlinear variations of these properties with respectto the atom number are observed. Comparative study of Raman spectroscopybetween PBE and B3LYP functionals is studied for each size of the consideredGQDs. Also, revolution of the G peak in each case has been separatelyinvestigated. All calculations are done by using the Gaussian 09W softwarepackage based on 3-21G Gaussian basis sets.