Are the experimentally observed 3-dimensional carbon honeycombs all-sp2 structures? The dangling p-orbital instability

Abstract

Recently, Krainyukova and Zubarev [Phys. Rev. Lett. 116, 055501 (2016)] reported that they observed a series of all-sp² 3-dimensional carbon honeycomb structures with interesting storage properties. In the present study we show that these structures are unstable, reducing to honeycomb structures with sp³ atoms at the honeycomb junctions. As we show, this instability is due to solitary electrons which occupy the unhybridized p orbitals of the junction atoms, thus violating the octet rule. These orbitals are localized and have all the features that characterize dangling orbitals. This instability, as well as the ability of unhybridized p orbitals to form dangling bonds, has not been reported previously.