First-principles investigation of structural, elastic, anisotropic, dynamic, electronic, thermo-physical, and optical properties of two-dimensional trigonal M2N (M = V, Nb, Ta) compounds for advanced technological applications

Abstract

In this study, the structural, mechanical, elastic, electronic, optical, and thermophysical properties of two-dimensional trigonal M₂N (M = V, Nb, Ta) compounds have been investigated using first-principles calculations based on density functional theory. The optimized lattice parameters were found to be a = b = 2.861, 3.142, and 3.085 Å, c = 4.390, 4.412 and 4.840 Å for V₂N, Nb₂N, and Ta₂N, respectively, which are in good agreement with available theoretical data. The formation enthalpies of −1.10 eV/atom (V₂N), −0.99 eV/atom (Nb₂N), and −0.72 eV/atom (Ta₂N) confirm their thermodynamic stability. The elastic constants fulfil the Born stability criteria, and the bulk modulus, shear modulus, and Young's modulus values indicate high mechanical hardness. The B/G ratios (1.76–2.42) suggest that all compounds exhibit ductile behaviour. The electronic band structure confirms the metallic nature of the M₂N compounds, with density of states analysis revealing the dominance of transition metal d-states near the Fermi level. The phonon dispersion curves do not contain any negative frequencies, ensuring dynamic stability. Optical properties show a high reflectivity in the ultraviolet region, indicating potential for optoelectronic and coating applications. These results suggest that M₂N compounds are promising materials for mechanical, thermal, and electronic device applications.