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

Abstract

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 Γ 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.

Flat-band engineering in tight-binding models: Beyond the nearest-neighbor hopping

“…V, artificial materials are promising candidates, due to the tunability of the hopping parameters. For solid-state systems, recent studies of first-principles calculations imply that carbon-based materials [65][66][67][68] , and pyrochlore oxides 69 will be promising candidates. Although the exact flatness will be spoiled by the additional hoppings in the real solid-state systems, our method will serve as a good starting point to search the materials with nearly flat bands penetrating the dispersive bands, which also show the intriguing physics.…”

Flat bands and higher-order topology in polymerized triptycene: Tight-binding analysis on decorated star lattices

“…Since three C 6 rings on each triptycene molecule form 120-degree structure, it is possible to construct a twodimensional network of triptycene molecule by placing them on a honeycomb lattice and connecting the neighboring C 6 rings by other molecules, such as acenes [16] or phenyls [17]. We call the materials thus obtained as polymerized triptycene.…”

Momentum-selective optical absorption in triptycene molecular membrane

“…38,39 There are two types of cross-linked structure in TMMs according to the bonding shape of each bridge, i.e., zigzag and armchair types. The recent first-principles calculations based on density functional theory (DFT) have shown that these TMMs are thermodynamically stable and become semiconducting with multiple Kagome bands, 40,41 i.e., several sets of graphene energy bands with a flat energy band. Especially, these multiple Kagome bands provide a good platform of selective excitation of electrons with specific momentum, i.e., at K and K ′ points.…”