Quantum chemical calculations have predicted the existence of a new carbon family with double-layered structures formed by arranging prism-C-2n. (n = 6, 8, and 12) units. Theoretical explorations of potential energy surfaces suggest the lowest barriers of the reaction channels to be ca. 30 kJ mol(-1) for a D-2h prismC16 dimer and a D-3h prism-C-24 trimer. Geometry optimizations under periodic boundary conditions yield some prism-C-2n, sheets composed of CC single bonds of ca. 0.15-0.16 nm. The relative energies per one atom with respect to graphene are 90-160 kJ mol(-1). Van der Waals thickness is estimated to be ca. 0.5 nm. (C) 2015 Elsevier B.V. All rights reserved.