First principles study of the structural, mechanical, phonon, optical, and thermodynamic properties of half-Heusler (HH) compound NbFeSb

We studied the structural, mechanical, phonon, optical and thermodynamic properties of MgAgAs-based NbFeSb compound by means of first-principles based on the density functional theory. The calculated lattice constant is in good agreement with the available experimental data. The electronic structure and corresponding density of states (DOS) were also calculated to give insight into the bonding mechanism and an indirect band gap was observed as similar to 1.77 eV, which is significantly higher than the previously reported one (0.529 eV). The elastic properties such as shear modulus, Young's modulus etc under pressure, up to 65 GPa, were analyzed. The phonon dispersion curves, one-phonon DOS, and optical properties were obtained. In addition, the thermodynamic properties such as heat capacity, Debye temperature etc of NbFeSb were calculated at various temperatures and pressures by applying the quasi-harmonic Debye model.