Structures and electron states of (4,4)CNT-graphene hybrid system through DFTB investigation

Abstract

Self-consistent density functional tight binding (SCC-DFTB) algorithm is performed to investigate the connection of a (4,4) carbon nanotube and graphene having topological defects. The examined seamless coupling CNT-graphene configurations are characterized by packing geometries, bond length, bonding energy, chemical potential, HOMO-LUMO energy gap, Mulliken populations on atoms, charge density differences, and molecular orbitals on HOMO and LUMO energy levels. Simulation results show that coupling models among the bottom atoms of the tube and the graphene atoms around the defect as well as defect patterns greatly affect configurations and electrical structures of coupled systems. Graphene having some defective patterns improves high possibility for strongly bonding the tubes. Apparent charge transfer occurs among the atoms in the tubes and graphene, and differences of transferred charges can be also found in the coupling modes. In addition, for the atoms at the connecting knots, their s and p orbitals present significant differences in the abilities of losing and gaining charge. Charge density differences as well as molecular orbitals on the HOMO and LUMO energy levels indicate the bonding between the tube and graphene as well as electron’s distribution in space.