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In the present work we used the experimental relative volume unit cell and the elastic stiffness constants measured by Speziale et al. (Journal of Geophysical Research, Vol. 111, (2006), pp. B02203 (12 pages)) using the Radial X-Ray Diffraction at high pressure from 5.6 up to 65.2 GPa to investigate the effect of high pressure on the bulk modulus, aggregate shear modulus, elastic wave velocities and Debye temperature of calcium oxide (CaO) ceramic material in cubic rock-salt (B1) phase. Our obtained values show that the bulk modulus increases monotonously with increasing pressure, while the aggregate shear modulus, the mean elastic wave velocity and the Debye temperature of CaO material varied non-linearly and non-monotonously with increasing pressure from 5.6 up to 65.2 GPa.

Based on the experimental ground state parameters reported in the literature (Luo et al., Phys. Rev. B 50 (1994)16232-16237); in the present work we reproduce the variation in the volume with the pressure up to 40 GPa for calcium sulfide (CaS) compound, which criticized in cubic rock-salt structure. We used two different models of equation of state (EOS); the fist is the model of Vinet, while the second one is the EOS Murnaghan’s model. We studied also the effect of the pressure on the crystal density. We established some analytical models relating the volume with the pressure, as well as the crystal density with the pressure.Finally, we predicted the melting point, the Debye temperature and the sound velocity of CaS material, which are 1202.2 K, 423.7 K, and 4049.5 m/s, respectively.  Â

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%.

First-principles calculations are performed to study the structural and elastic properties, sound velocities, and Debye temperature of rocksalt-structured copper monochloride (CuCl) and copper monobromide (CuBr). The structural parameters, elastic constants, longitudinal, transverse, and average elastic wave velocities, and the Debye temperature in the pressure range 10–20 GPa are successfully predicted and analysed. The variation of the elastic constants and bulk modulus as a function of pressure is found to be non-linear for CuCl and almost linear for CuBr. Based on the obtained values of the elastic constants, the bulk modulus, the isotropic shear modulus, Young’s modulus, Poisson’s ratio, and Pugh’s ratio of the aggregate materials are also investigated. The analysis of Poisson’s and Pugh’s ratios shows that these materials become ductile for pressures in the range 10–20 GPa. The evolution of the longitudinal sound velocity under pressure indicates the hardening of the corresponding phonons in both materials.

Density functional theory, density functional perturbation theory, and the Debye model have been used to investigate the structural, elastic, sound velocity, and thermodynamic properties of AlN with cubic rock-salt structure under high pressure, yielding the equilibrium structural parameters, equation of state, and elastic constants of this interesting material. The isotropic shear modulus, Pugh ratio, and Poisson’s ratio were also investigated carefully. In addition, the longitudinal, transverse, and average elastic wave velocities, phonon contribution to the thermal conductivity, and interesting thermodynamic properties were predicted and analyzed in detail. The results demonstrate that the behavior of the elastic wave velocities under increasing hydrostatic pressure explains the hardening of the corresponding phonons. Based on the elastic stability criteria under pressure, it is found that AlN with cubic rock-salt structure is mechanically stable, even at pressures up to 100 GPa. Analysis of the Pugh ratio and Poisson’s ratio revealed that AlN with cubic rock-salt structure behaves in brittle manner.

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 pseudopotential plane wave method based on the density functional theory has been employed to study some thermodynamic properties of copper chloride (CuCl) and copper bromide (CuBr) compounds under the effect of temperature and pressure. The phase transition pressure, the unit cell volume, the isothermal bulk modulus, the constant volume heat capacity, the entropy, the Debye temperature, the Gruneisen parameter and the volumetric thermal expansion coefficient are studied in the pressure range 0–10 GPa, and for temperatures ranging from 0 K up to 650 K and 750 K for CuCl and CuBr, respectively. The phase transition pressure is found to be around 7.8 and 6.95 GPa for CuCI and CuBr, respectively. These values are respectively in reasonably good agreement with the experimental ones of 8.2 GPa and 6.8 GPa reported in the literature. Moreover, at room temperature and zero pressure, the heat capacity at constant volume and the Gruneisen parameter of both compounds of interest are found to be in good agreement with the available experimental and theoretical data. The information gathered from the present investigation may be useful for the study of the behavior of the fundamental properties of CuCI and CuBr under the influence of high temperature and pressure.

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.

Pseudopotential plane-wave method (PP–PW) based on density functional theory (DFT) and density functional perturbation theory (DFPT) within the Teter and Pade exchange-correlation functional form of the local spin density approximation (LSDA) is applied to study the effect of pressure on the elastic and piezoelectric properties of the (B3) boron–bismuth compound. The phase transition, the independent elastic stiffness constants, the bulk modulus, the direct and converse piezoelectric coefficients, the longitudinal, transverse, and average sound velocities, and finally the Debye temperature under pressure are studied. The results obtained are generally lower than the available theoretical data (experimental data are not available) reported in the literature.

The pseudopotential plane-wave method in the framework of density functional theory with the generalized gradient approximation for the exchange-correlation functional has been adopted to calculate the phase stability and thermodynamic properties of BSb under high pressure and temperature. The BSb compound transforms from the most stable zinc-blende phase to the rock-salt one and the pressure of the phase transition is around 60 GPa, which is in excellent agreement with the available theoretical data. The thermodynamic properties, such as bulk modulus, heat capacity, entropy, thermal expansion coefficient, Debye temperature, and Gruneisen parameter of BSb with stable zinc-blende structure are determined in the temperature range of 0–1200 K and the pressure up to the phase transition pressure. In addition, the electronic polarizability, plasmon energy, microhardness, melting temperature, and the thermal conductivity at 300 K are also predicted for BSb in zinc-blende structure. It is believed that these results will be quite helpful not only to understand the investigated properties of this less studied compound but also useful for the future applications in semiconductor based devices.

The principal goal of this work is the prediction only by means of some emperical formulas and two other physical quantities (the bond length and the bulk modulus calculated initially from first-principle calculations) of the refractive index, the exciton Bohr parameter, the electronic polarizability, the plasmon energy, the force constants, the optical band gap energy, the homopolar and heteropolar energies , the bonding-antibonding energy gap, the ionicity, the dielectric constant, and the optical susceptibility of (B3) thallium phosphide (TlP) compound. In addition, the Debye temperature, the melting temperature, the thermal conductivity and finally the linear thermal expansion of this compound are also obtained. Our results are in general in good agreement with the previous results of the literature. Keywords : Optical Properties, Thermal Properties, TlP Compound.

In the present work, we report ?rst principles calculations of the near-neighbor distance (bond length) and the average energy gap using the pseudopotential plane wave method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) and the Hartwigzen-Goedecker-Hutter (HGH) scheme for the pseudopotential of Boron- Bismuth compound in its structure zincblende phase. The refractive index, the plasmon energy, the force constants, the lattice energy, the homopolar and heteropolar energies, the ionicity, the linear optical susceptibility, the hardness, the dielectric constants, the Debye temperature and the melting temperature are then predicted by mean of some simple emperical formulas. The results obtained are analyzed and compared with the available theoretical data of the literature Keywords : Optoelectronic and Thermal Properties, BBi Compound.

We present an Ab-initio study of the pressure effect on the structural properties of thallium phosphide (TlP) compound. The plane-wave pseudopotential approach to the density functional theory (DFT) within the local density approximation (LDA) implemented in Abinit code was used. The equilibrium lattice parameter, bulk modulus and its pressure derivatives, crystal density, near-neighbor and nearest-neighbor distances are calculated. The threshold pressure of the phase transition, the volume collapses and the Debye temperature are also obtained. Our results are in general in very good agreement with the previous results of the literature. Keywords : PP-PW Approach, Structural Properties, TlP Compound.