Motivated by the recent experimental realization of a two-dimensional (2D) BeN₄ monolayer, in this study we investigate the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN₄ using first-principles calculations. The calculated phonon band dispersion reveals the dynamical stability of a free-standing BeN₄ layer, while the cohesive energy indicates the energetic feasibility of the material. Electronic band dispersions show that monolayer BeN₄ is a semi-metal whose conduction and valence bands touch each other at the Σ point. Our results reveal that increasing the layer number from single to six-layers tunes the electronic nature of BeN₄. While monolayer and bilayer structures display a semi-metallic behavior, structures thicker than that of three-layers exhibit a metallic nature. Moreover, the optical parameters calculated for monolayer and bilayer structures reveal that the bilayer can absorb visible light in the ultraviolet and visible regions better than the monolayer structure. Our study investigates the electronic properties of Dirac-semimetal BeN₄ that can be an important candidate for applications in nanoelectronic and optoelectronic.

The fabrication of the C₆N₇ monolayer [Zhao et al., Sci. Bull. 66, 1764 (2021)] motivated us to discover the optical, structural, mechanical, and electronic properties of the C₆N₇ monolayer by employing the density functional theory (DFT) method. We find that the shear modulus and Young's modulus of the C₆N₇ monolayer are smaller than the relevant values of graphene. However, Poisson's ratio is more significant than that of graphene. Applying the PBE (HSE06) functional bandgap of the C₆N₇ monolayer is 1.2 (1.97) eV, and the electronic dispersion is almost isotropic around the Γ point. C₆N₇ is more active in the ultraviolet region as compared to the visible light region. This study provides outstanding results, highlighting the bright viewpoints for the applications of the C₆N₇ monolayer in electronic and optical systems.