In this paper, we have investigated the structural, elastic, optoelectronic and thermoelectric properties of the new half-Heusler alloys TiXSb (X: Ru, Pt) and Ti 2 RuPtSb 2 double half-Heusler compound, using the full-potential linearized augmented plane wave method. Different approximations for the exchange-correlation functional were performed as generalized gradient approximation + Hubbard potential (GGA + U) and its combination with the modified Becke-Johnson potential. The negative values of the calculated formation energy indicate that these compounds are energetically stable. Both half Heusler alloys are halfmetallic ferromagnetic materials and exhibit an integer magnetic moment of Mt = 1.00 μ B .While, the Ti 2 RuPtSb 2 is a direct semiconductor at center symmetry. The calculations of optical properties revealed that Ti 2 RuPtSb 2 compound exhibits an excellent optical efficiency. The thermoelectric properties such as the Seebeck coefficient (S); electronic thermal conductivity (κ e /τ), power factor (PF), and figure of merit (ZT) have been studied and discussed in detail. Consequently, the investigated compounds were identified as candidate materials for high technological applications.

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The full-potential linear muffin-tin orbital method (FP-LMTO) within the local density approximation (LDA) using the Perdew-Wang parameterization is used to calculate the structural, electronic and elastic properties of the filled skutterudite CeOs 4 P 12 . The results of the electronic properties show that this compound is an indirect band gap material (Γ-N). A special interest has been made to the determination of the elastic constants since there have been no available experimental and theoretical data. The energy band gaps and their volume and pressure dependence are also investigated.Keywords: Skutterudite, FP-LMTO, electronic properties, elastic constants. IntroductionThe pursuit of new and interesting strongly correlated electron phenomena has led to a systematic investigation of the rare earth-based filled skutterudite compounds. This pursuit has been driven by the remarkable fact that one can observe metal insulator transitions [1], magnetic order [2], heavy fermion behaviour [3], superconductivity [4,5,6,7], quadrupolar ordering [8,9,10], Kondo insulating behaviour [11], non-Fermi liquid behaviour [12], quantum critical points [13,14], and heavy fermion superconductivity all in the same family of compounds [3]. The filled skutterudite compounds have the general formula MT 4 X 12 (M = alkali metal, alkaline-earth, lanthanide, or actinide; T = Fe, Ru, or Os; and X = pnictogen such as P,

Herein, a comprehensive computational investigation of the stability and mechanical, electronic, and thermal transport properties of two new Tl‐based MAX‐phase compounds Ta2TlC and Ta2TlN is presented. The negative values of the formation energy ensure the chemical stability of the materials. Moreover, the analysis of phonon dispersion and elastic constants shows that the compounds are dynamically and mechanically stable. From the electronic structures, the miss of bandgap at the Fermi level reveals the metallic nature of the compounds, and state densities indicate the difference between the conductivities of the two compounds. Furthermore, interestingly low thermal conductivities are obtained for both compounds. Finally, the ambition is that this report will inspire new theoretical and experimental studies on these compounds.

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