In this study, the full potential linearized augmented plane wave method with the GGA approximation was employed to study the structural, elastic, electronic and thermal properties of the novel intermetallic REPt$_4$In$_4$ (RE$=$Eu,Gd, Tb, Dy, Ho) compounds. Our findings demonstrate that the equilibrium lattice parameters are in good agreement with the available experimental measurements. The elastic constants ($C_{\rm ij}$) were also calculated to understand the mechanical properties and structural stability of the compounds. Furthermore, the density of states and the charge density distributionsof the compounds were calculated to understand the nature of the bonding in the material. Our analysis of the calculated values of the Poisson’s ratio and the $B/G$ ratio shows their ductile structure. Additionally, the temperature-dependent thermodynamic parameters are computed by the quasi-harmonic Debye model in the range of 0–600 K, where the primitive cell volume and thermal expansion coefficients have been obtained successfully. Consequently, this study on the structural, elastic, bonding and thermal properties of REPt$_4$In$_4$ intermetallic compounds demonstrate that these compounds can be used as potential candidates in the domain of energy storage and electronic devices.

In this study, an analysis of the effect of Na substitution on the electronic, structural and thermoelectric (TE) properties of the Li$_2$CuAs material is presented. The study is performed by employing the full-potential linearized augmented plane wave plus local orbital method designed within the density functional theory. To carry out the calculations related to the band structure, generalized gradient approximation by Wu-Cohen (WC-GGA) in combination with Trans Blaha-modified Becke-Johanson mBJ (TB-mBJ) potential is employed. Our results at the level of the WC-GGA approach show that there is no bandgap, whereas, at the level of the TB-mBJ approximation, the material displays bandgap with Na substitution, which is found to be further increased with the increasing Na concentration. To understand the role of different electronic states on the bandgap structure, the total and partial densities of states are also analysed. Furthermore, the temperature effect on the Seebeck coefficient, electronic thermal conductivity, electrical conductivity, power factor and figure of merit are computed. Our obtained results of the TE properties of Li$_2$CuAs at different Na compositions suggest that this compound is a potential candidate for thermoelectricity.