Structural, electronic, magnetic, and optical investigations of sodium chalcogenides: First-principles calculations

The electronic, magnetic, and optical properties of NaS and NaSe compounds have been studied by using first-principles calculations based on density-functional theory and full-potential linearized augmented plane-wave method. The Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and modified Becke–Johnson (mBJ-GGA) have been used to deal with the exchange-correlation potential. The PBE-GGA and mBJ-GGA electronic calculation of the spin-up configuration shows an insulating behavior, while the spin-down shows a metallic behavior. In addition, both PBE-GGA and mBJ-GGA agree that the total magnetic moment per unit cell for these compounds is 1 μB. From optical calculations, we see that ε1(0) value in the spin-up channel is positive, which shows an insulating character, while it has a large negative value for the spin-down configuration, which shows a metallic character. The NaS and NaSe refractive index n(ω) indicates a metallic demeanor as the real and imaginary parts of the dielectric constant.