Study on the geometrical structures,electronic structures,magnetic properties and edge effects of graphene and hexagonal boron nitride nanosheets

This research was performed by first-principles calculations based on the density functional theory (DFT). The properties of graphene and h-BN nanosheets with different sizes were calculated. The quantum size effect and edge effect are studied systematically. In the calculations, we constructed the n × n (n = 6, 7, 8, ..., 24) supercells and took out one of the largest regular hexagon or approximate hexagonal nanosheets from the supercells. In order to increase the stability of the structure, each atom in the structure must form a six-atom ring with other atoms. The diameter of the largest nanosheet is about 5.5 nm, containing 816 atoms. The geometrical structures, electronic structures, magnetic properties and electron distributions of the edge are discussed. The results show that outermost atoms of the nanosheets are more likely to change positions, to make the edge of the nanosheets smoother. For the electronic structures, with the increasing size of the nanosheets, the energy levels change from discrete to continuous. For the magnetic properties, the total magnetic moments increase with the size of the nanosheets. The magnetic moments of the nanosheets are mainly located on the outermost atoms. In the investigation of charge doping, when additional electrons are added to the nanosheets, the total magnetic moments will decrease. Further calculations show that the added electrons are mainly distributed on the outermost at-oms. The added electrons are filled in the breaking bonds of the atoms on the edge of the nanosheets, thereby causing the magnetic moments to disappear. The results are also given when electrons are subtracted from the nanosheets. (authors)