DFT formalism studies on the structural and electronic properties of hexagonal graphene quantum dot with B, N and Si substitutional impurities

The study of carbon-based nanostructured materials is a highly active research field, that has made significant progress in the study of twodimensional materials and nanotechnology. The interest in these materials is mainly attributed to the fascinating properties they exhibit, as seen in the case of graphene as a 2D material, as well as emergence on numerous novel 2D materials and their heterostructures. Additionally, there is important interest in systems such as 2D quantum dots. Therefore, this work focuses on the systematic study of graphene quantum dots of various sizes, all within the framework of first-principles density functional theory. We started with the simplest graphene quantum dot (GQD) structure, benzene (C6H6), which consist of six carbon atoms passivated with hydrogen atoms. We then increased its size by adding more aromatic rings, resulting in the following GQD configurations: C24H12, C54H18, C96H24, C150H30 and C216H36. We report the density of states (DOS) and the imaginary part of the dielectric function (ε2) for the system, analyzing both the pristine configuration and the effect of both single and double (boron, nitrogen and silicon, denoted as Sa). The double substitutional atom study was done considering random, ortho-, meta-, and para-director positions just for the C94H24Sa2 GQD. In general, we can conclude that as the GQD increases in size, the HOMO-LUMO energy decreases. Furthermore, it is observed that boron and nitrogen exhibit their expected n-, and p-type doping characteristics, but this differs between single and double Sa substitutions. Additionally, the imaginary part of the dielectric function is highly sensitive to the positions of single and double substitutional atoms, as well as the polarization of incident light. Therefore, we suggest that these differences can be used to clearly determinate the type of substitutional atoms and their positions from optical measurements.