electronic properties of various graphene quantum dot structures: an ab initio study

Density functional theory (dft) and thermal dft (thdft) calculations were used to evaluate the energy band structure, bandgap, and the total energy of various graphene quantum dots (gqds). the dft calculations were performed using local density approximation for the exchangecorrelation functional and normconserving pseudopotentials. we consider the triangular and hexagonal gqds with zigzag and armchair edges and 13 nm dimensions with many hundred atoms. the simulation results show that all of these gqds are direct bandgap semiconductors with a flat band structure, and they are suitable for electronics and optoelectronics applications. analysis of gqds in which the a and b sublattice symmetries were broken showed degenerate zeroenergy shells. using the thdft calculations carried out at temperatures up to 1400 k, we evaluated the temperature dependence of the gqds bandgaps and total energies via entropyterm and electron’s kinetic energy. the obtained results indicate that the groundstate dft calculations are valid for determining the electronic properties of gqds up to room temperature. moreover, we tune semiempirical parameters of the tightbinding model by the dft results in small gqds to reduce the computational cost of electronic structure calculations for large gqds, which contained up to thousands of atoms.

Electronic Properties of Various Graphene Quantum Dot Structures: an Ab Initio Study

Density functional theory (DFT) and thermal DFT (thDFT) calculations were used to evaluate the energy band structure, bandgap, and the total energy of various graphene quantum dots (GQDs). The DFT calculations were performed using local density approximation for the exchangecorrelation functional and normconserving pseudopotentials. We consider the triangular and hexagonal GQDs with zigzag and armchair edges and 13 nm dimensions with many hundred atoms. The simulation results show that all of these GQDs are direct bandgap semiconductors with a flat band structure, and they are suitable for electronics and optoelectronics applications. Analysis of GQDs in which the A and B sublattice symmetries were broken showed degenerate zeroenergy shells. Using the thDFT calculations carried out at temperatures up to 1400 K, we evaluated the temperature dependence of the GQDs bandgaps and total energies via entropyterm and electron’s kinetic energy. The obtained results indicate that the groundstate DFT calculations are valid for determining the electronic properties of GQDs up to room temperature. Moreover, we tune semiempirical parameters of the tightbinding model by the DFT results in small GQDs to reduce the computational cost of electronic structure calculations for large GQDs, which contained up to thousands of atoms.