First-principles calculations of the electronic, optical and elastic properties of CdIn₂S₄ thiospinel at ambient and elevated pressure

CdIn₂S₄ thiospinel was studied by means of first-principles calculations in both generalized gradient and local density approximations (GGA and LDA). One of the main results of this paper is that the controversy regarding the character of the CdIn₂S₄ band gap previously encountered in the literature was clearly resolved in favor of the indirect gap. The calculated density of states was compared with the experimental XPS spectrum; very good agreement was demonstrated. The structural, electronic, optical and elastic properties were calculated in the pressure range of 0 to 10 GPa, below the pressure of phase transition for this compound. The estimated pressure coefficient of the band gap of 0.071/0.063 eV GPa^-1 (GGA/LDA) is in excellent agreement with the experimental data of 0.076 or 0.069 eV GPa^-1 found in the literature. The calculated pressure dependence of the unit cell volume follows the experimental results very closely. The dependence of the interionic distances, lattice parameter and all elastic constants on pressure was calculated. Refined estimations of the Debye temperature for CdIn₂S₄ are given as 280 K (LDA) and 252 K (GGA). The elastic anisotropy of CdIn₂S₄ was visualized by plotting the three-dimensional dependence of the Young's modulus on a direction in the crystal lattice; it was established that the lowest Young's moduli are realized if the external stress is applied along the crystallographic axes.