Structural properties of a three-dimensional all-sp2phase of carbon

We have studied the structural properties of a recently proposed, hypothetical, all-${\mathit{sp}}^2$ phase of carbon, using the first-principles pseudopotential total-energy method. Our results are compared with those of an earlier tight-binding calculation. While the two calculations yield equilibrium volumes and bond lengths that are in excellent agreement, there are discrepancies in the cohesive energy, elastic constants, and predicted stability of this phase.