Structural, electronic, and optical properties of 2D $\alpha$-graphdiyne from first-principles

Abstract

The structural, electronic, and optical properties of monolayer $\alpha$-graphdiyne ($\alpha$-GDY) are systematically investigated using density-functional theory within the plane-wave pseudopotential formalism. The electronic band structure reveals a gapless Dirac crossing at the K point, indicating Dirac-semimetallic behavior within the PBE/GGA framework. The calculated total and orbital-projected density of states show that the electronic states near the Fermi level are dominated by the carbon $2p$ orbitals, while the contribution of the $2s$ orbitals is comparatively weak. The optical response exhibits pronounced polarization dependence. The in-plane dielectric function displays a strong low-energy electronic response and negative values of its real part, whereas the out-of-plane component remains positive throughout the investigated energy range. Consistently, the absorption coefficient, extinction coefficient, reflectivity, and electron energy-loss spectra reveal pronounced optical anisotropy. The calculated plasma frequencies are approximately $3.21$~eV for in-plane polarization and $1.06$~eV for out-of-plane polarization, highlighting the strongly anisotropic electronic response of the monolayer. These findings demonstrate that $\alpha$-GDY combines Dirac-like electronic behavior with highly anisotropic optical properties, indicating its potential relevance to polarization-sensitive optoelectronic, plasmonic, and nanoelectronic applications.

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