Tight-binding Hubbard Model Calculation Of The Density Of States (DOS), Magnetic Properties And Optical-absorption Properties For Graphene Quantum Dot Systems

In this paper, using a tight-binding Hubbard type model for the πelectrons, we investigate the magnetism and optical absorption properties ofcharge neutral hexagonal graphene quantum dots (GQDs) terminated withzigzag edges. Within the Hartree-Fock approximation and taking intoaccount the long-range Coulomb interaction, our calculation yields aferromagnetic ground state with magnetic moments localized on the edgesfor GQDs, and also gives an antiferromagnetism state with energy very closeto the ferromagnetism ground state. We find that both the ferromagnetic andthe antiferromagnetic states have stripe patterned charge densitydistributions as a result of the long-range Coulomb interaction. The opticalconductivity for GQDs has an energy gap in the low frequency regime incontrast to the bulk neutral graphene sheet where a universal constant isapproached.