The atomic structure and electronic and magnetic properties of two zig-zag-edged hexagonal nanohelicenes of the second type [1.2] and [2.2] were studied by the density functional theory. These objects possess a helical periodicity and belong to the fifth family of line symmetry groups in their global energy minimum. These nanohelicenes were shown by us to be diamagnetic metals that undergo spontaneous symmetry breaking into antiferromagnetic semiconductors as a result of the Mott-Hubbard metal-insulator transition. However, under some torsional stress, a reversible transformation to a diamagnetic metal can take place, which is promising for the use of nanohelicenes in electro-magneto-mechanical nanodevices.
Keywords: DFT; graphene spiral; helical symmetry; helicene; line symmetry groups; metal-insulator transition; spontaneous symmetry breaking.