First-principles calculations of Electronic Structure of Novel 2D Nanostructures: a DFT, GGA-PBE functional and hybrid functional HSE06 study

In this paper, the structural, electronic, optical, and photocatalytic properties of MXene monolayers are studied. MXenes are a new class of two-dimensional (2D) transition metal carbides and nitrides with the chemical formula Mn+1Xn (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; X = C, N; n = 1–3) that etching MAX phases have recently synthesized. We study Hf2CO2 and Zr2CO2 nanostructures, comparing them with the GGA-PBE and HSE06 functionals. These calculations were performed using density functional theory (DFT). The unit cell of these structures and their atomic positions are fully optimized. The results show that the lattice constants for two-dimensional nanostructures Hf2CO2 and Zr2CO2 are 3.3592 and 3.3771 angstroms, respectively. The band gap of these nanostructures is of the indirect type. Based on the information obtained, their band gap values with GGA-PBE functional are 0.92 and 0.89 eV, respectively. The results of calculations with HSE06 hybrid functional show that both Hf2CO2 and Zr2CO2 nanostructures are semiconductors with band gaps of 1.75 and 1.72 eV. It can be seen that with an HSE06 hybrid functional, the amount of band gap improves. The real and imaginary parts of the dielectric function have been calculated to investigate the optical properties of these structures. In addition, the studied materials have high absorption in visible and ultraviolet regions. The obtained results show that these nanostructures may apply in designing optoelectronic devices.