A theoretical study of the structural, elastic, electronic, mechanical, and thermal properties of the perovskite-type hydride CaNiH 3 is presented. This study is carried out via first-principles full potential (FP) linearized augmented plane wave plus local orbital (LAPW+lo) method designed within the density functional theory (DFT). To treat the exchangecorrelation energy/potential for the total energy calculations, the local density approximation (LDA) of Perdew-Wang (PW) and the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) are used. The three independent elastic constants (C 11 , C 12 , and C 44 ) are calculated from the direct computation of the stresses generated by small strains. Besides, we report the variation of the elastic constants as a function of pressure as well. From the calculated elastic constants, the mechanical character of CaNiH 3 is predicted. Pertaining to the thermal properties, the Debye temperature is estimated from the average sound velocity. To further comprehend this compound, the quasi-harmonic Debye model is used to analyze the thermal properties. From the calculations, we find that the obtained results of the lattice constant (a 0 ), bulk modulus (B 0 ), and its pressure derivative (B 0 ) are in good agreement with the available theoretical as well as experimental results. Similarly, the obtained electronic band structure demonstrates the metallic character of this perovskite-type hydride.
The phase stability and electronic properties in Al 3 Ta compound are studied using the FP-LAPW method. In this approach, the generalized gradient approximation (GGA) is used for the exchange-correlation potential calculation. The total energy calculations show that the D 022 structure is more stable than that of D 023 and L1 2. The densities of states exhibit a pseudo gap near the Fermi level for all considered structures. By analyzing the electronic charge density we find a build-up of electrons in the interstitial region, and the bonds are directed from the Ta atoms to the Al atoms, which is the characteristic of covalent bonding. The temperature and pressure effects on the structural parameters, Debye temperature, Grüneisen parameter, heat capacities (Cv, Cp) and thermal expansion are predicted through the quasi-harmonic Debye model.
The ab-initio calculations based on the density functional theory (DFT) have been performed to study the structural, mechanical, electronic, thermal and thermodynamic properties of Al3Sc and Al3Ti binary compounds and their ternary mixture Al3(Sc[Formula: see text]Ti[Formula: see text]) in L12 and D0[Formula: see text] structures. The total energy calculations show that the L12 structure is the more stable one. The Al3Sc[Formula: see text]Ti[Formula: see text] undergoes a martensitic transformation and the formation enthalpies and the lattice parameters decrease with increasing concentration x. The elastic constants are determined and the results show that all compounds are mechanically stable and the cubic cells are more easily deformed by shearing than by unidirectional compression. The elastic modulus indicates that the addition of Ti atoms to Al3Sc improves its ductility. The densities of states (DOSs) calculations show the strong spd hybridization which leads to the formation of a pseudo-gap near the Fermi level in ternary alloys. The densities of states at the Fermi level N(E[Formula: see text]) confirm the phase stability. The quasi-harmonic Debye model is used to predict the thermal properties such as heat capacity, Debye temperature, Grüneisen parameter and thermal expansion coefficient of the considered alloys. The determination of Gibbs free mixing energy at different concentrations has been used to calculate the T–x diagram.
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