Abstract
We predict the existence and dynamical stability of heptagraphene, a new graphitic structure formed of rings of 10 carbon atoms bridged by carbene groups yielding seven-membered rings. Despite the rectangular unit cell, the band structure is topologically equivalent to that of strongly distorted graphene. Density-functional-theory calculations demonstrate that heptagraphene has Dirac cones on symmetry lines that are robust against biaxial strain but which open a gap under shear. At high deformation values bond reconstructions lead to different electronic band arrangements in dynamically stable configurations. Within a tight-binding framework this richness of the electronic behavior is identified as a direct consequence of the symmetry breaking within the cell which, unlike other graphitic structures, leads to band gap opening. A combined approach of chemical and physical modification of graphene unit cell unfurls the opportunity to design carbon-based systems in which one aims to tune an electronic band gap.
Highlights
We predict the existence and dynamical stability of heptagraphene, a new graphitic structure formed of rings of 10 carbon atoms bridged by carbene groups yielding seven-membered rings
Backed up by detailed calculations of the electronic and mechanical properties of the density functional theory (DFT) ground state, we have provided theoretical insight of a new C-based nanostructure formed by ten-membered rings bridged by carbene groups
With only four C atoms participating in the formation of the bands in the vicinity of the Fermi level, an effective structure resembling that of highly strained graphene was found as responsible of the Dirac point in off-set with respect to a high-symmetry point in the Brillouin zone (BZ)
Summary
We predict the existence and dynamical stability of heptagraphene, a new graphitic structure formed of rings of 10 carbon atoms bridged by carbene groups yielding seven-membered rings. As in metallic carbon nanotubes, the conduction and the valence bands touch each other at particular points of the Brillouin zone (BZ) forming the so called Dirac cones, where the energy is directly proportional to the electron momentum. This allows electrons to be considered as massless particles and behave as relativistic charge carriers. One of the main goals of this papers is to demonstrate that changing graphene unit cell from hexagonal to rectangular may lead to the creation of Dirac cones and band gap opening upon additional application of shear stress
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