Possible nonplanar structure of phagraphene and its thermal stability

It is shown that phagraphene, a recently predicted planar allotropic form of graphene with Dirac fermions, is unstable or, at least, almost unstable with respect to transverse atomic displacements in the monolayer. This result is obtained by numerical calculations in the framework of both the tight-binding model and the density functional theory. A nonplanar atomic configuration of phagraphene has a wavy shape and is nearly degenerate in energy with respect to the planar configuration. The main types of possible structural defects in phagraphene are determined. The temperature dependence of characteristic times of their formation is found.