Prediction of an ultrasoft graphene allotrope with Dirac cones
Abstract Searching for the Dirac materials with ultrasoftness is crucial for flexible electronics applications. Based on first principles calculations, we propose a new carbon allotrope (named as ph graphene) with a penta hexagonal framework, which is energetically more favorable than the penta graphene composing surely of pentagons and some of already synthesized carbon allotropes. Ph graphene has an in plane stiffness of 27.75 GPa*nm, smaller than those of graphene and penta graphene by one order. The famous isotropic Dirac cones are well preserved in the ultrasoft ph graphene, exhibiting delocalized feature of p z orbits with the Fermi velocity of 2.8 x 10 5 m/s. Additionally, surface hydrogenation alters drastically the electronic and mechanical properties of ph graphene, resulting in electronic spin polarization and anisotropic negative Poisson's ratios sequentially with the increase of hydrogenation concentrations.