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Barium chalcogenides are known for their high-technological importance and great scientific interest. Detailed studies of their elastic, mechanical, dynamical and thermodynamic properties were carried out using density functional theory and plane-wave pseudo potential method within the generalized gradient approximation. The optimized lattice constants were in good agreement when compared with experimental data. The independent elastic constants, calculated from a linear fit of the computed stress–strain function, were used to determine the Young’s modulus (E), bulk modulus (B), shear modulus (G), Poisson’s ratio ([Formula: see text]) and Zener’s anisotropy factor (A). Also, the Debye temperature and sound velocities for barium chalcogenides were estimated from the three independent elastic constants. The calculations of phonon dispersion showed that there are no negative frequencies throughout the Brillouin zone. Hence barium chalcogenides have dynamically stable NaCl-type crystal structure. Finally, their thermodynamic properties were calculated in the temperature range of 0–1000 K and their constant-volume specific heat capacities at room-temperature were reported.

In this work, details density functional theory calculations were performed to obtain the electronic, elastic, phonon and thermodynamic properties of half-Heusler alloys HfNiX (X = Ge and Sn). The PBE functional as implemented in Projector augmented-wave (PAW) pseudopotentials was used for all the calculations. From our results, we reported the energy gap of 0.38 eV for HfNiSn and 0.61 eV for HfNiGe indicating the semiconductor property of these compounds. Also, the mechanical and elastical stabilities of these compounds were confirmed from the comparison of the elastic constants of these compounds with conditions for stabilities. Although the phonon dispersion curves for HfNiGe and HfNiSn are similar with splitting at the Γ point, the shift in their frequency was as a result of the mass different in Ge and Sn. The phonon dispersion curve predicts the dynamically stabilities of these half-Heusler alloys. From the thermodynamic properties of these compounds, it was revealed that these compounds are soft at low temperature, but at a high temperature they tend to be hard materials. Our calculations showed that these two compounds are mechanically, elastically and dynamically stable as cubic half-Heusler alloys.

The mixing properties of liquid Al–Au alloys with respect to the concentration of each constituent is determined using a method based on hard sphere system and pseudo-potential perturbation. These models were used to get relevant information on mixing properties of the Al–Au alloys like the Gibbs energy and the entropy of mixing. The concentration fluctuations, chemical short range order for the hard sphere mixture (quasi-lattice theory) and the activity are calculated to know the extent of order in the liquid alloys. The results revealed that there is a degree of ordering in liquid Al–Au alloy (hetero-coordinated).

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The ab initio method is used to calculate the electronic, elastic, lattice-dynamic, and thermoelectric properties of the semimetal Half-Heusler compound HfIrAs. Density Functional Theory within Generalized Gradient Approximation is used to carry out calculations of lattice parameters, band structure, electronic density of states, phonon band structure, phonon density of states, elastic moduli, specific heat at constant volume, the Seebeck coefficient, electrical conductivity, the power factor, and the dimensionless figure of merit. The electronic band structure reveals that the compound is semimetal. The phonon dispersion shows that HfIrAs is dynamically stable. The projected phonon density of states, which shows the contribution of each constituent atom at every frequency level, is also reported. The ratio of bulk modulus to shear modulus is 2.89; i.e., the material is ductile, and it satisfies stability criteria. The thermoelectric properties of this compound at different temperatures of 300 K, 600 K, and 800 K are reported as a function of hole concentration for the first time to the best of our knowledge. The dimensionless figure of merit of HfIrAs is 0.57 at 800 K when the doping concentration is 0.01×1020 cm−3. Therefore, this compound is predicted to be a good thermoelectric material.

Adopting Density Functional Theory (DFT) with Hubbard U correction implemented in Quantum Espresso, we have performed a comprehensive first-principles study of MPSe3 (M = Cd. Fe and Ni) monolayers. The computed electronic properties revealed the semi-conductive nature of the monolayers with small indirect bandgaps. A free-standing single layer of MPSe3 can be exfoliated from the parent compound by virtue of its structural stability and high in-plane stiffness. Hence, the elastic and dynamical properties were computed to establish the mechanical and dynamical stability. The results showed that CdPSe3 and NiPSe3 are stable in the trigonal structure while a single negative frequency observed in the phonon dispersion of FePSe3 indicates the possibility to relax to another, less symmetric structure. In addition, these 2D systems showed relatively good response when subjected to strain hence, they can be said to be mechanically stable. The thermodynamic properties, such as internal energies, vibrational free energies, entropies and constant-volume heat capacities have been computed within the harmonic approximations using the phonon density of states. The computed thermoelectric properties show that CdPSe3 and FePSe3 have the peak figure of merit at low temperature of 50K. This work predicts a thermoelectric performance with an electronic figure of merit of 0.28 for p-doped CdPSe3. Moreover, the DFT+U method predicts an electronic figure of merit of 0.39 and 0.2 for p-doped FePSe3 and NiPSe3, respectively.

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