Narrow Results

The potential applications of the cubic phase of CsNbO₃ perovskite have been explored by examining its elastic, electronic, and photocatalytic characteristics using a first-principles approach. The structural robustness when subjected to pressure has been verified by studying the computed elastic constants. Its substantial elastic moduli, hardness, and toughness values propose its suitability for various engineering applications. A transition from flexibility to fragility is observed at pressures exceeding 10GPa. The CsNbO₃ material demonstrates an indirect and narrow band gap, making it a promising candidate in optoelectronic applications. Changes in the band gap due to pressure indicate adjustments in orbital hybridization. The material’s low effective carrier mass and high carrier mobility anticipate favorable electrical conductivity. Assessments of the potentials at the conduction band (CB) and valence band (VB) edges underscore the remarkable capacity of CsNbO₃ for activities such as water-splitting and promoting sustainable energy production.

The electronic, elastic, acoustic and optical properties of fluorite phase TiO₂ are calculated by using the first principles method. Different exchange-correlation functionals are used with the ultrasoft plane wave pseudopotential method under pressure from 0 GPa to 90 GPa. The calculated values of the lattice constant, cell volume, bandgap, bulk modulus and the pressure derivative of bulk modulus are in agreement with the prior published results. The calculated elastic parameters show that the fluorite structure is mechanically stable, the ratio of bulk to shear modulus indicates that it is brittle, and pressure derivative of the bulk modulus shows that it is not a super hard material, but a hard material. The longitudinal and transverse acoustic velocities in the direction [100], [110] and [111] are computed by using prior determined data. Besides, the optical properties are also studied under the aforementioned range of pressure, and the results show more photolytic activity over the other phases.

The mechanical property of alloys plays a vital role in applications. In order to probe the mechanical property of the Zr–Ti alloy, we have successfully generated a 16-atom special quasi-random structure (SQS) at concentration 0.5 for the Zr–Ti alloy (${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$) with supercell ($2\times 2\times 2$) based on the hcp Bravais cell, which has the same shape with the hcp Bravais cell. Such an SQS can be used as a good template at the 0.5 concentration of all binary hcp random alloys as the initial step for the further description of their alloy properties. Our calculated bulk modulus of ${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$ is 101.7GPa, falling within the region for the extreme two constituents $({\mathrm{\text{B}}}_0^{\mathrm{\text{Zr}}}<$ B${}_0^{\mathrm{\text{Zr}}{}_8\mathrm{\text{Ti}}{}_8}<$ B${}_0^{\mathrm{\text{Ti}}}$). Obtained $B∕G$ of ${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$ (3.60) is significantly larger than those of Zr (2.75) and Ti (2.64), which means that the ductility of ${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$ alloy is better than those of its constituents. The maximum Cauchy stress of ${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$ is 20.53GPa at strain ($\epsilon )=0.43$ in [0001] direction. In addition, this SQS template for ${\mathrm{\text{Zr}}}_8{\mathrm{\text{Ti}}}_8$ has been proved to be mechanically stable.

Topological insulators (TI) are immensely investigated due to their promising characteristics for spintronics and quantum computing applications. In this regard, although bismuth, telluride, selenide and antimony containing compounds are typically considered as topological insulators, materials with Hg₂CuTi-type structure have also shown their potential for TIs as well. Here, we present first principles study of the Y₂RuPb compound, pertaining to its structural, mechanical, electrical and the optical properties. Calculations are executed at the level of the parameterized Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA), employing the full-potential (FP) linearized muffin-tin orbital (LMTO) approach, as designed within the density functional theory (DFT). The study is carried out on the Hg₂CuTi-type and Cu₂MnAl-type structures of the Y₂RuPb compound. From our structural calculations, it is found that Y₂RuPb is more stable in its Hg₂CuTi-type structure; however, the analysis of the mechanical properties reveals its stability in both phases against any kind of elastic deformation. Similarly, Dirac cone shaped surface energy levels found in the predicted electronic band structure of the Y₂RuPb compound, and good agreement of the obtained results with Zhang et al., demonstrates that it is a topological insulating material. Additionally, the real and imaginary parts of the dielectric function $\epsilon$ ($\omega$) and refractive index n ($\omega$), for an energy range up to 14eV, are analyzed as well.

The phonon, elastic and thermodynamic properties of L1₂ phase Rh₃Zr have been investigated by density functional theory approach combining with quasi-harmonic approximation model. The relaxed lattice parameters of L1₂ phase Rh₃Zr at zero pressure are in good agreement with the experiment. To judge the stability of L1₂ phase Rh₃Zr under high pressure, the phonon band structure has been studied. The results show that L1₂ phase Rh₃Zr possesses dynamical stability in the pressure range from 0GPa to 80GPa due to the absence of imaginary frequencies. The pressure dependences of elastic constants $C_{ij}$ have been analyzed. All the elastic constants of Rh₃Zr in a wide pressure range (0–80GPa) meet general mechanical conditions, suggesting that L1₂ phase Rh₃Zr is mechanically stable under pressure up to 80GPa. L1₂ phase Rh₃Zr exhibits ductility under high pressure and the pressure can improve the ductility from the results of the value of $B∕G$ and Poisson’s ratio $\nu$. Hence, it is obvious that the mechanical properties of Rh₃Zr can be improved under high pressure. Moreover, we have obtained the thermodynamic properties using the quasi-harmonic Debye model. We note that the effect of the temperature on the Debye temperature ${\mathrm{\Theta }}_D$ is smaller than that of the pressure. We believe that our result will be a good guidance to future works and applications.

A study of the crystal structure, mechanical and acoustic properties of two $P{2}_1∕a$ and $P{2}_1∕c$ monoclinic phases of naphthalene and anthracene was performed using ab initio method of linear combination of atomic orbitals (LCAO) and basis sets: C_6-21G*, H_3-1p1G. The method was implemented in the CRYSTAL${}^{\prime }$14,${}^{\prime }$17 software package using electron density functional theory including van der Waals interactions (DFT-D2 and DFT-D3 (BJ)), in the local density approximation (LDA) with VWN exchange-correlation potential, gradient approximation PBE exchange-correlation functional and B3LYP hybrid functional. The calculated elastic constants for the first time are in moderate agreement with experimental data. Bulk modulus $B$, shear modulus $G$, Young’s modulus $E$ and the Poisson’s ratio $\mu$, as well as acoustic properties (average velocity of sound $〈v〉$, the Debye temperature ${\mathrm{\Theta }}_D$, and acoustic Grüneisen parameter ${\gamma }_a$) were obtained using the Voigt–Reuss–Hill model.

The effects of vacancies on the strength and elastic constants of silicon, such as Young's modulus and Poisson's ratio are investigated using the molecular dynamics simulations with the Stillinger–Weber potential. The defected crystalline cells contain randomly generated defect distributions in the simulation models. The ideal strength is found to be 33.6 GPa at the strain 0.26. The Young's modulus and Poisson's ratio is 148 GPa and 0.252, respectively. It is found that the strength decreases as the point defect fraction increases, and the variation of the strength versus the point defect fraction coincides with a decaying exponential function. In addition, vacancies are shown to reduce the elastic constants. In general, the elastic constants of silicon vary linearly versus the defect fraction.

Using plane wave pseudopotential calculations and the generalized gradient approximation, we have studied the structural, elastic, and electronic properties of Hf₂SnC and Hf₂SnN. Lattice parameters and equilibrium volume are in satisfactory agreement with the experimental values. Electronic properties show a metallic character of both compounds. Bonds are originally made from hybridized Hf d–Cp (or N p) states, and Hf d–Snp states, confirmed by strong coupling between Hf–C (or N), and Hf–Sn bonding from the charge density distribution.

In the present paper, a new relationship for the pressure dependences of elastic constants is developed by using a new expression for the pressure dependence of bulk modulus and a method developed by Grover et al. The proposed relationship is applied to study elastic constants of MgO, NaCl, CaF₂, and CaO. The results obtained for elastic constants are found in good accordance with the experimental and first-principle results.

The all-electron full-potential linearized muffin-tin orbital method, by means of quasi-harmonic Debye model, is applied to investigate the elastic constant and thermodynamic properties of body-centered-cubic tantalum (bcc Ta). The calculated elastic constants of bcc Ta at 0 K is consistent with the previous experimental and theoretical results. Our calculations give the correct trends for the pressure dependence of elastic constants. By using the convenient quasi-harmonic Debye model, we refined the thermal equations of state. The thermal expansivity and some other thermal properties agree well with the previous experimental and theoretical results.

The higher-order perturbation theory based on pseudopotential approach is used to investigate few elastic and vibrational properties of Group IV semiconductors. The homogeneous deformation method is used to calculate elastic constants. To consider electron-ion interactions, our own proposed potential is employed to investigate such properties of Si, Ge and α-Sn. The potential contains only single parameter and its value is determined by fitting experimental value of bulk modulus. The calculated physical properties like elastic constants, pressure derivatives of the bulk modulus, pressure derivatives of elastic constants, Young's modulus and Poisson's ratio etc., of Si, Ge and α-Sn are in good agreement with available experimental and other available theoretical results. The deviation of the present calculations using our potential with respect to experimental data is found to be less than 10% in most of the calculated physical properties. To consider the exchange and correlation effect, five different local-field correction functions are incorporated in the present investigations. From the present study, it can be observed that incorporation of local-field correction and the covalent-correction term are important in such type of investigations.

We evolve an effective interionic interaction potential (EIoIP) to investigate the pressure induced phase transitions from Zinc blende (B3) to Rocksalt (B1) structure in ZnSe semiconductor. The developed potential consists of the long-range Coulomb and three-body interactions (TBI) and the Hafemeister and Flygare type short-range (SR) overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction. The three-body interactions arise from the electron-shell deformation when the nearest-neighbor ions overlap and has been employed for detailed studies of pressure-induced phase-transition behavior of ZnSe semiconductors. Our calculated value of the phase transition pressure (P_t) is higher and the magnitude of the discontinuity in volume at the transition pressure is consistent with reported data. The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. It is inferred that the vdW interaction is effective in obtaining the Debye temperature, Gruneisen parameter, thermal expansion coefficient and compressibility. It is argued that the model with TBI (model II) has yielded somewhat more realistic predictions of the phase-transition and high-pressure behavior as compared to usual two-body potentials (model I) based on phenomenological approach.

In the frame of density functional theory, first-principles calculations have been carried out to investigate the structures, elastic constants, structural phase transition between B1 and B2 phases and thermodynamic properties of the zirconium nitride (ZrN) by means of the generalized gradient approximation. The equilibrium lattice parameter we obtained for ZrN in B1 phase is closer to the experiment results than previous theoretical results. In addition, the calculations of the elastic constants show that ZrN is a brittle material. What is more, based on third-order natural strain equation of state, the phase transition pressure 338 GPa for ZrN is predicted for B1–B2 transition. According to the quasi-harmonic Debye model, the thermodynamic parameters of ZrN have been investigated systematically.

Physical properties like elastic constants, pressure derivative of bulk modulus, pressure derivative of elastic constants and acoustic wave velocities in different directions for Mg_xZn_1-xS, Mg_xZn_1-xSe and ZnS_ySe_1-y semiconductor ternary alloys and Mg_xZn_1-xS_ySe_1-y quaternary alloys with different concentrations of x and y are studied using our previously proposed potential based on the pseudopotential formalism. It is noticed from the present study that the physical properties under investigations depend on concentrations x and y of constitute compounds. The present results of various physical quantities of compounds presented here are compared with the available experimental data and other theoretical estimations and showed roughly reasonable agreement. The numerical values of same quantities for ternary alloys and MgZnSSe quaternary alloys were reported first time and hence such results may be useful for comparison purpose in future with either the experimental or the theoretical work.

The structural, elastic, thermal and electronic properties of perovskite hydrides SrLiH₃ and SrPdH₃ have been investigated using the all-electron full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The present results are in good agreement with available theoretical and experimental data. The three independent elastic constants $(C_{11}$, $C_{12}$ and $C_{44})$ are also reported. From electronic band structure and density of states (DOSs), it is found that SrLiH₃ is an insulator characterized by an indirect gap of 3.48 eV, while SrPdH₃ is metallic with a calculated DOSs at Fermi energy of 0.745 states/eV-unit cell. Poisson’s ratio $(\sigma )$, Young’s modulus (E), shear modulus (G), anisotropy factor (A), average sound velocities $(v_m)$ and density $(\rho )$ of these compounds are also estimated for the first time. The Debye temperature is deduced from the average sound velocity. Variation of elastic constants and bulk modulus of these compounds as a function of pressure is also reported. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.

In this paper, the formation energies and elastic constants of $\alpha$-Al₂O₃, MgO and AlN in both rock salt (cubic) and wurtzite (hexagonal) structures were investigated by first principles calculations. The results show that the formation energy being −17.8, −6.3, −3.06 and −3.46 eV/formula unit for $\alpha$-Al₂O₃, MgO, AlN (rock salt) and AlN (wurtzite). It suggests that in the ground state, $\alpha$-Al₂O₃ is relatively more stable than MgO and AlN. The elastic properties for a polycrystalline in the ground state were calculated with the obtained elastic constants, the elastic properties reveal the rock salt structure AlN is the hardest particles among all the inclusions, and all of these inclusions are classified as brittle materials, which is detrimental to the ductile nature of aluminum matrix. The calculated anisotropy index shows that the AlN (wurtzite) and $\alpha$-Al₂O₃ have a lower degree of anisotropy compared with MgO and AlN (rock salt). The calculated results are in good agreement with the values of experimental and other works.

In this paper, we have developed relationship to predict temperature dependence of elastic constants for geophysical minerals by using a formulation for volume dependence of isothermal Anderson–Grünesien parameter which is valid up to extreme compression limit $P\to \infty$ or $V\to 0$. An alternative formulation based on thermal pressure or thermal energy has also been used for determining elastic constants as a function of temperature. The basic idea used in this study is to generalize the expression of bulk modulus for determining temperature dependence of elastic constants. The results thus obtained for MgO, CaO, Mg₂SiO₄ and Al₂O₃ from the two different methods are very close to each other and also experimental data. The good agreement reveals the validity of the formulations given in this study.

The structural, electronic, elastic and thermodynamic properties of Curium Monopnictides CmX (X = N, P, As, Sb and Bi) are investigated using first-principles calculations based on the density functional theory (DFT) and full potential linearized augmented plane wave (FP-LAPW) method under ambient condition and high pressure. The exchange-correlation term is treated using two approximations spin-polarized local density approximation (LSDA) and spin-polarized generalized gradient approximation generalized (GGA). The structural parameters such as the equilibrium lattice parameters, bulk modulus and the total energies are calculated in two phases: namely NaCl (B1) and CsCl (B2). The obtained results are compared with the previous theoretical and experimental results. A structural phase transition from B1 phase to B2 phase for Curium pnictides has been obtained. The highest transition pressure is 122 GPa for CmN and the lowest one is 10.0 GPa for CmBi compound. The electronic properties show that these materials exhibit half-metallic behavior in both phases. The magnetic moment is found to be around 7.0 $\mu$B. The mechanical properties of CmX (X = N, P, As, Sb and Bi) are predicted from the calculated elastic constants. Our calculated results are in good agreement with the theoretical results in literature. The effect of pressure and temperature on the thermodynamic properties like the cell volume, bulk modulus and the specific heats C${}_{𝜗}$ and C${}_P$, the entropy ${𝒮}$ and the Grüneisen parameter $\gamma$ have been foreseen at expanded pressure and temperature ranges.

The band structure of Al${}_x$Ga${}_{1-x}$Sb semiconducting ternary alloys and their related properties such as elastic constants, microhardness, transition pressure to the first phase, acoustic wave velocities and melting temperature have been investigated. The calculations are performed using a pseudopotential approach within the virtual crystal approximation which includes the effect of compositional disorder as an effective potential. Generally, our results are found to be in good accord with the experimental results. The composition dependence of all features of interest showed a monotonic behavior and suggests that the stiffness, hardness and structural stability becomes better in Al${}_x$Ga${}_{1-x}$Sb for higher Al concentrations. The bulk sound speeds and melting temperature are found to become larger when increasing the Al content.

The aluminum-based intermetallic compounds AlZr₃, AlCu₃ and AlCu₂Zr are studied for elastic and mechanical properties by a DFT embodied in WIEN2k code with Generalized Gradient Approximation (GGA) as an exchange correlation functional. The cubic elastic parameters $C_{11}$, $C_{12}$ and $C_{44}$ are found keeping bulk modulus value the same as in the structural optimization. The mechanical properties such as Young’s modulus, shear modulus, anisotropic factor and Poisson’s ratio are then found using these fundamental parameters. It is found that our calculated results are in good agreement with available theoretical and experimental results.