University of Tabriz Tabriz Journal of Electrical Engineering 2008-7799 51 2 2021 07 23 Electronic Properties of Various Graphene Quantum Dot Structures: an Ab Initio Study Electronic Properties of Various Graphene Quantum Dot Structures: an Ab Initio Study 213 220 13620 FA M. Ghandchi Department of Electronics, Mechanics, Electrical and Computer Engineering Faculty, Science and Research Branch, Islamic Azad University, Tehran, Iran 0000-0002-3308-2781 Gh. Darvish Department of Electronics, Mechanics, Electrical and Computer Engineering Faculty, Science and Research Branch, Islamic Azad University, Tehran, Iran M. K. Moravvej-Farshi Department of Electronics, Faculty of Electrical and Computer Engineering, Nano-Plasmo Photonic Research Group, Tarbiat Modares University, Tehran, Iran Journal Article 2020 05 15 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 exchange-correlation functional and norm-conserving pseudopotentials. We consider the triangular and hexagonal GQDs with zigzag and armchair edges and 1-3 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 zero-energy 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 entropy-term and electron’s kinetic energy. The obtained results indicate that the ground-state DFT calculations are valid for determining the electronic properties of GQDs up to room temperature. Moreover, we tune semi-empirical parameters of the tight-binding 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. 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 exchange-correlation functional and norm-conserving pseudopotentials. We consider the triangular and hexagonal GQDs with zigzag and armchair edges and 1-3 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 zero-energy 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 entropy-term and electron’s kinetic energy. The obtained results indicate that the ground-state DFT calculations are valid for determining the electronic properties of GQDs up to room temperature. Moreover, we tune semi-empirical parameters of the tight-binding 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. https://tjee.tabrizu.ac.ir/article_13620_4fbc030174db9671d7c77f6266659458.pdf