Abstract
We have performed quantum Monte Carlo calculations to study the cohesion
energetics of carbon allotropes, including sp3-bonded diamond, sp2-bonded
graphene, sp-sp2 hybridized graphynes, and sp-bonded carbyne. The comput- ed
cohesive energies of diamond and graphene are found to be in excellent
agreement with the corresponding values de- termined experimentally for diamond
and graphite, respectively, when the zero-point energies, along with the
interlayer binding in the case of graphite, are included. We have also found
that the cohesive energy of graphyne decreases system- atically as the ratio of
sp-bonded carbon atoms increases. The cohesive energy of γ-graphyne, the most
energetically- stable graphyne, turns out to be 6.766(6) eV/atom, which is
smaller than that of graphene by 0.698(12) eV/atom. Experi- mental difficulty
in synthesizing graphynes could be explained by their significantly smaller
cohesive energies. Finally we conclude that the cohesive energy of a
newly-proposed two-dimensional carbon network can be accurately estimated with
the carbon-carbon bond energies determined from the cohesive energies of
graphene and three different graphynes.