FP-LAPW investigation of mechanical and thermodynamic properties of Na₂X (X = S and Se) under pressure and temperature effects

Structural, elastic and thermodynamic properties of sodium chalcogenides (Na₂X, X = S, Se) have been calculated using FP-APW+1o method. The ground state lattice parameter, bulk moduli have been obtained. The Zener anisotropy factor, Poisson’s ratio, shear modulus, Young’s modulus, have also been calculated. The calculated structural and elastic constants are in good agreement with the available data. We also determined the thermodynamic properties, such as heat capacities C_V and C_P, thermal expansion α , entropy S, and Debye temperature θ_D, at various pressures and temperatures for Na₂X compounds. The elastic constants under high pressure and temperature are also calculated and elaborated.