J Comput Electron DOI 10.1007/s10825-017-1008-5 A computational study of the optoelectronic and thermoelectric properties of HfIrX (X = As, Sb and Bi) in the cubic LiAlSi-type structure S. Chibani 1 · O. Arbouche 2 · K. Amara 3 · M. Zemouli 3 · Y. Benallou 1 · Y. Azzaz 2 · B. Belgoumène 3 · M. Elkeurti 3 · M. Ameri 2 © Springer Science+Business Media New York 2017 Abstract We have systematically investigated the struc- tural, electronic, optical and thermoelectric properties of HfIrX (X = As, Sb and Bi) belonging to the 18 valence electron ABX family using first-principles density functional theory calculations. In the first phase, the structural parame- ters of HfIrX (X = As, Sb and Bi) in the cubic LiAlSi-type (F-43 m) structure such as the lattice parameters, the bulk modulus ( B ) and their pressure derivative ( B ′ ) are calcu- lated using the full-potential linearized augmented plane wave method within the generalized gradient approximation GGA-PBEsol. In the second phase, investigations of elec- tronic and optical properties were treated by the TB-mBJ exchange-correlation potentials. The third phase is devoted to the interpretation and prediction of the thermoelectric per- formance of our compounds by combining the results of ab initio band structure calculations and Boltzmann transport theory in conjunction with rigid band and constant relaxation time (τ) approximations as incorporated in the BoltzTraP code. We note that, because of the existence of heavy ele- ments in our compounds, spin–orbit coupling is added for both electronic and thermoelectric calculations in order to test the effect of spin–orbit interaction on these properties. Our results are compared with other theoretical and experi- mental data and provide guidance for practical applications in the fields of optoelectronics and thermoelectrics. B O. Arbouche arbouche_omar@yahoo.fr 1 Technology Laboratory of Communication, Dr. Tahar Moulay University of Saïda, 20000 Saïda, Algeria 2 Laboratory Physico-Chemistry of Advanced Materials, Djillali Liabes University of Sidi Bel-Abbes, 22000 Sidi Bel Abbes, Algeria 3 Laboratory of Physico-Chemical Studies, Dr. Tahar Moulay University of Saïda, 20000 Saïda, Algeria Keywords ABX ternary compounds · HfIrX · FP-LAPW · GGA-PBEsol · TB-mBJ · Spin–orbit coupling · Electronic structure · Optical properties · Thermoelectric properties 1 Introduction Several studies of HfIrX (X = As, Sb and Bi) are available in the literature devoted to the topological phase transition, structural, electronic, optical and thermoelectric properties. Recently, Gautier et al. [1] examined the crystallographic data of the new stable 18 valance electron ABX ternary compounds which involve two different transition metals A and B and one sp X element with LiAlSi-type cubic struc- ture, and found that the lowest-energy crystal structures are thermodynamically stable. As the ABX structure with C 1b symmetry is far from compact, it may be subject to lat- tice instabilities, disorder generally occurs between d metals [2]. ABX materials, being semiconductors or in a semimetal state [3–7], are produced and examined with regard to many applications due to their excellent optical and thermoelectric properties for medium to high temperatures. In the present work, we study the structural, electronic, optical and trans- port properties of HfIrX (X = As, Sb and Bi) alloys using the full-potential linearized augmented plane wave (FP-LAPW) [8] based on density functional theory (DFT) [9] as imple- mented in the WIEN2k computer package [10] and the Boltzmann transport equation under the constant relaxation time approximation (RTA) [11–13] for charge carriers as implemented in the BoltzTraP code [14]. In this paper, we use computational methods to investigate the crystal struc- ture of HfIrX (X = As, Sb and Bi) and we calculate the bulk modulus ( B ), lattice constant (a), and derivatives of the bulk modulus ( B ′ ) of these compounds. The electronic structure results predict the band gaps of these compounds and show 123