Structural modulation of graphene by an external electric field

The geometric structure of graphene under an external electric field was investigated using the density functional theory (DFT). DFT calculations revealed that the hole injection into graphene highly modulates the geometric structure of graphene. The lattice parameter of graphene monotonically increased with increasing the hole doping concentration. The lattice constant is insensitive to the electron doping. The fragility and robustness against the hole and electron doping, respectively, are ascribed to the electronic structure of graphene under the electric field. The wave function analysis revealed that the holes are accommodated in the bonding π states, weakening covalent bonds between C atoms. In contrast, the electrons are primarily accommodated in nearly free electron states with a maximum amplitude above and below the graphene layer