Structural and electronic properties of nonconventional α -graphyne nanocarbons

Abstract

In this work, we propose a set of nonconventional graphyne lattices inspired by previously studied $s{p}^{2}$ nanocarbon sheets, known as haeckelites, and we study their electronic properties by density functional theory methods. Two of these systems are solely composed of five- and seven-membered rings in rectangular lattices, while a third system features a mixture of five-, six-, and seven-polygonal rings in a hexagonal network. We show that these systems exhibit dynamical, thermal, and mechanical stability as demonstrated by phonon band structures, molecular dynamics simulations, and by the computation of their elastic constants. The three lattices exhibit a metallic nature similar to their full-$s{p}^{2}$ counterparts. However, the graphynes' electronic properties are strongly different from those of the original haeckelites, as the largest contribution to their frontier states comes from the $sp$ hybridized atoms. Furthermore, the three proposed systems feature different electronic signatures from each other, as their frontier states feature different energy ranges for forbidden electronic states, and one of them features a set of Dirac-like cones.