  We report on various nanocarbons formed from a unique structural pattern
containing two pentagons, three hexagons and two heptagons, resulting from
local rearrange- ments 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 inter- connected 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 semi-metallic
conduction.
