  From density functional theory investigations helped with crystal chemistry
rationale, single-atom C, embedded in layered hexagonal CCn with n = 6, 12, 18
networks, is stable in a magnetic state with M(C)= 2 Bohr Magneton (BM). The
examined compositions, all inscribed within the P6/mmm 191 space group are
characterized as increasingly cohesive with n, figuring mono, bi and tri
layered honeycomb-like C networks respectively. The spin projected total
density of states shows a closely half-metallic behavior with a gap at minority
spins and metallic majority spins. Such results together with the large C-C
intersite separation and the integer 2 BM magnetization, let propose an
intra-band mechanism of magnetic moment onset on carbon 2p states. Support is
provided from complementary calculations assuming C2C12 structure with planar 2
C with d(C-C)= 2.46 Angstroms resulting into a lowering of the magnetization
down to 0.985 BM per C atom involving a ferromagnetic order arising from
interband spin polarization on C where one nonbonding spin polarizes whereas
the other is involved with the bonding with the other carbon. Further
illustrative proofs are provided with the magnetic charge density projected
onto the different atoms, showing its prevalence around C, contrary to the C6
layers, as well as electron localization function ELF.
