Rippled nanocarbons from periodic arrangements of reordered bivacancies in graphene or nanotubes.

We report on various nanocarbons formed from a unique structural pattern containing two pentagons, three hexagons, and two heptagons, resulting from local rearrangements around a divacancy in pristine graphene, or nanotubes. This defect can be inserted in sheets or tubes either individually or as extended defect lines. Sheets or tubes containing only this defect as a pattern can also be obtained. These fully defective sheets, and most of the tubes, present a very pronounced rippled (wavy) structure and their energies are lower than other structures based on pentagons and heptagons published so far. Another particularity of these rippled carbon sheets is their ability to fold themselves into a two-dimensional porous network of interconnected tubes upon heat treatment as shown by hybrid Monte Carlo simulations. Finally, contrary to the common belief that pentagon/heptagon based structures are metallic, this work shows that this defect pattern should give rise to semimetallic conduction.