Electronic Structure of Two-Dimensional Hydrocarbon Networks of sp2 and sp3 C Atoms

Gamma Based on density functional theory with the generalized gradient approximation, we have investigated the geometric and electronic structures of two-dimensional hexagonal covalent networks consisting of oligoacenes and fourfold coordinated hydrocarbon atoms, which are alternately arranged in a hexagonal manner. All networks were semiconductors with a finite energy gap at the Gamma point, which monotonically decreased with the increase of the oligoacene length. As a result of a Kagome network of oligoacene connected through sp(3) C atoms, the networks possess peculiar electron states in their valence and conduction bands, which consist of a flat dispersion band and a Dirac cone. The total energy of the networks depends on the oligoacene length and has a minimum for the network comprising naphthalene.