Beryllium nitride (Be₃N₂) graphene like monolayer and zigzag single walled nanotubes. A DFT exploration of their structural and vibrational properties

Abstract

We present a detailed density functional theory study of beryllium nitride Be₃N₂ in several periodic arrangements ranging from the 3D bulk, the 2D slab model to the 1D (n,0) zigzag single walled nanotubes using B3LYP hybrid functional and Gaussian-type basis sets. IR and Raman spectra are computed through a coupled-perturbed KS/HF scheme permitting identification of all arrangements. For (n,0) single-walled zigzag beryllium nitride nanotubes, the cohesive, rolling and relaxation energies, band-gaps, equilibrium geometries, polarizabilities and vibrational spectra are established where the trend towards the hexagonal monolayer (h- Be₃N₂) is explored. Their IR spectrum presents two frequency ranges (500–650 cm⁻¹) and (1350–1500 cm⁻¹) that tend towards the optical vibrational modes of the 2D h- Be₃N₂ layer. Four sets of active bands are observed in their Raman spectrum. The first set contains two Raman modes with vanishing wave numbers when the nanotube radius increases and found to be connected to the elastic constants C₁₂ and C₆₆ of the h- Be₃N₂ single layer. The second (300–700 cm⁻¹) and fourth (1200–1600 cm⁻¹) modes are intrinsic nanotube active modes that result from the periodic boundary condition along the circumference. The third set (800–1000 cm⁻¹) contains two phonon modes A’₁ and E’₁ that tend to the Raman active mode E_2g of the 2D monolayer. This theoretical contribution should motivate new experimental works dealing with the design and optimization of low-dimensional beryllium nitrides.

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