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The influence of pressure and temperature on the thermodynamic properties of MgCu intermetallic compound was investigated by quasi-harmonic Debye model approximation. The equation of state (EoS) parameters has performed using plane-wave pseudopotential (PW-PP) approach in the framework of the density functional theory (DFT) and the generalized gradient approximation (GGA) for the exchange-correlation functional. Our results agree well with other data of the literature.The finite temperature thermophysical properties under pressure up to 16 GPa and high temperature up to 800 K, respectively were determined. Our results of the thermophysical properties are also agree very well with other data of the literature, where for example at ambient temperature, the deviation between our obtained value (11.05 Cal mol−1 K−1) of CV, and the theoretical value (11.21 Cal mol−1 K−1) reported in the literature is only around 1.44%. The finite temperature thermophysical properties were found varied monotonically with either temperature or pressure. Compared with other materials previously studied, similar behaviors were observed. Keywords: Thermophysical properties, Quasi-harmonic Debye model, MgCu intermetallic compound, High-pressure

The pseudopotential plane-wave approach in the framework of the density functional theory, and the density functional perturbation theory with the generalized gradient approach for the exchange-correlation functional has been used to calculate the structural phase stability, elastic constants and thermodynamic properties of boron - arsenide (BAs) compound. The BAs compound transforms from the zincblende phase to rock-salt structure; the phase transition pressure was found to be 141.2 GPa with a volume contraction of around 8.2%. The thermodynamic properties under high pressure and temperature up to 125 GPa and 1200 K respectively were also determined, analyzed and discussed in comparison with other data of the literature. The systematic errors in the static energy were corrected using the bpscal EEC method. Our results agree well with those reported in the literature, where for example, our calculated melting temperature (2116 K) deviates from the theoretical one (2132.83 K) with only 0.8%, and the deviation between our result (1.86) of the Gruneisen parameter and the theoretical one (1.921) is only around 3.2%.

A systematic ab initio investigation has been performed to determine the elastic stability, the structural and finite-temperature thermodynamic properties of copper iodide (CuI) in the zinc-blende phase under pressure. All calculations are carried out based on the pseudopotential density functional method, in which we employ the generalized gradient approximation of the revised Perdew-Burke-Ernzerhof form and local density approximation of Ceperly and Adler parameterized by Perdew and Zunger together with plane-wave basis sets for expanding the periodic electron density. The obtained normalized volume dependence of the pressure and the equation-of-state parameters including equilibrium volume, isothermal bulk modulus and its pressure derivatives are in excellent agreement with the experimental data and other theoretical results. The elastic constants are calculated and the investigation of the mechanical stability from the elastic constants under pressure indicates that the zinc-blende CuI is stable up to 10 GPa. Through the careful evaluation with the quasi-harmonic Debye model in which the phononic effects are considered, a complete set of thermodynamic data up to 800 K, including the bulk modulus, volume thermal expansion coefficient, heat capacity, entropy, Debye temperature, and Gruneisen parameter of CuI with zinc-blende structure is achieved. This set of data is considered as the useful information to understand the high-temperature and high-pressure properties of CuI.

The pressure-induced B3-B1 structural phase transition and some interesting thermodynamic properties for high-pressure B1 structure of cubic copper iodide (CuI) have been studied systematically using first-principles calculations based on density functional theory. It is found that CuI has a B3 ground-state phase at zero pressure and the transition pressure from B3 to B1 structure determined by the relative enthalpy versus pressure curves is about 6.9 GPa with a volume contraction of 14.42%. As a high-pressure phase, the B1 structure will be mechanically stable up to 57 GPa according to the generalized elastic stability criteria. Through the quasi-harmonic Debye model, the dependences of the primitive cell volume, isothermal bulk modulus, volumetric thermal expansion coefficient, heat capacity, entropy, and Debye temperature of CuI with high-pressure B1 phase on pressure and temperature are successfully predicted. The thermodynamic properties are summarized in the pressure range of 0–50 GPa and the temperature up to 800 K.

A study of the high-pressure elastic properties of new synthetic Ir 2 P in the anti-fluorite structure is conducted using ab initio calculations based on density functional theory. The elastic constants C 11 , C 12 and C 44 for the cubic Ir 2 P are obtained by the stress-strain method and the elastic stability calculations under pressure indicate that it is stable at least 100 GPa. Additionally, the electronic density of states, the aggregate elastic moduli, that is bulk modulus, shear modulus, and Young's modulus along with the Debye temperature, Poisson's ratio, and elastic anisotropy factor are all successfully obtained. Moreover, the pressure dependence of the longitudinal and shear wave velocities in three different directions [100], [110], and [111] for Ir 2 P are also predicted for the first time.

The phase transition of boron arsenide (BAs) has been studied by means of a density-functional theory calculation. Features such as structural phase stability, elastic properties, sound velocity, Debye temperature and melting temperature have been obtained at zero and high pressures. The transition pressure ( P t ) of the material of interest from zinc-blende to NaCl phase has been determined and found to agree well with experiment. At pressures lower than P t the zinc-blende phase is found to be thermodynamically and mechanically more stable than the NaCl phase. The mechanical behavior has been studied in terms of ductility and brittleness by means of different methods and found to differ only on the exact border between the two types of mechanical behaviors. The behavior of the longitudinal sound velocity under pressure indicated the softening of its corresponding phonons.

Kamel et al. (2016) [1] have recently published a paper in Optik 127 (2016) 4559–4573. They have studied several interesting properties, such as: structural, elastic, electronic, optical and thermodynamic properties of copper halides (CuCl, CuBr and their ternary alloys CuCl 1−x Br x (0.0 ≤ x ≤ 1.0)) using full-potential linear muffin-tin orbital (FP-LMTO) method. After carefully reading the paper of Kamel et al. (2016), it is observed that the algebraic values of the longitudinal ( v l ), transverse ( v t ) and average ( v m ) wave velocities, and also that of the Debye temperature θ D , of CuX (X = Cl, Br) binary compounds obtained in the paper Kamel et al. (2016) [1] are not correctly calculated. Although this mistake has no influence on the conclusion of the paper Kamel et al. (2016) [1], I think, that is better to correct the numerical values of the previous quantities, which can be reused in the future by other researchers, perhaps for comparison or for other object. In the present work, I recalculate the correct numerical values of the longitudinal ( v l ), transverse ( v t ) and average ( v m ) wave velocities, and the Debye temperature θ D , of CuX (X = Cl, Br) compounds, using the lattice parameters and the elastic moduli obtained in the original work of Kamel et al. (2016) [1].

The finite temperature thermophysical quantities are one of the most important properties of solids and have become the subject of significant interdisciplinary interest in recent years. We report a detailed theoretical investigation on the equation of state (EoS) parameters, electronic polarizability and finite temperature thermophysical properties of aluminum phosphide using plane-wave pseudopotential approach in the framework of the density functional theory within the generalized gradient approximation. Our results regarding EoS parameters and electronic polarizability are found to be in good accord with previous data reported in the literature. Moreover, using the model of the quasi-harmonic Debye approximation plus empirical energy corrections, the thermophysical properties for temperatures up to 2000 K are examined and discussed. Our findings show that the thermophysical properties vary monotonically with either temperature or pressure which is consistent with the trends previously reported in the literature.