Size dependence in the stabilities and electronic properties of \alpha -graphyne and its BN analogue

TL;DR

This study predicts the stability, structural transformations, and electronic properties of -graphyne and -BNyne materials of various sizes, revealing size-dependent stability and the presence of Dirac cones, with potential applications in electronics.

Contribution

First-principles calculations of stability and electronic properties of size-dependent -graphyne and -BNyne, including structural transformations and effects of hydrogenation.

Findings

-graphyne(n) and -BNyne(n) are stable for even n, unstable for odd n.

-graphyne(3) undergoes a structural transformation breaking hexagon symmetry.

Dirac cones exist in all -graphyne sizes, with decreasing Fermi velocities.

Abstract

We predict the stabilities of \alpha-graphynes and their boron nitride analogues(\alpha-BNyne), which are considered as competitors of graphene and two-dimensional hexagonal BN. Based on first-principles plane wave method, we investigated the stability and structural transformations of these materials at different sizes using phonon dispersion calculations and ab-initio finite temperature, molecular dynamics simulations. Depending on the number of additional atoms in the edges between the corner atoms of the hexagons, n, both \alpha-graphyne(n) and \alpha-BNyne(n) are stable for even n, but unstable for odd n. \alpha-graphyne(3) undergoes a structural transformation, where the symmetry of hexagons is broken. We present the structure optimized cohesive energies, electronic, magnetic and mechanical properties of stable structures. Our calculations reveal the existence of Dirac cones in the electronic structures of \alpha-graphynes of all sizes, where the Fermi velocities decrease with increasing n. The electronic and magnetic properties of these structures are modified by hydrogenation. A single hydrogen vacancy renders a magnetic moment of one Bohr magneton. We finally present the properties of the bilayer \alpha-graphyne and \alpha-BNyne structures. We expect that these layered materials can function as frameworks in various chemical and electronic applications.