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The structural, elastic and electronic properties of A₂C₂ (A = Li, Na, K, Rb and Cs) at zero temperature were investigated by first-principles total energy calculations. The optimized equilibrium structural parameters agree well with available experimental values. Elastic constants, bulk modulus, Young's modulus and Poissons ratio were given. All the structures studied are stable mechanically and all stable A₂C₂ studied has strong compressibility, which originates from weak Coulomb repulsion between metal atoms and carbon atoms. The electronic structure calculations show that binary alkali metal carbides studied here are insulators.

In a nuclear reactor, the Zr–$x$Nb alloy, which is used as a structural material in the core region, is irradiated by energetic particles that cause the atoms to be displaced from their lattice sites and giving rise to crystal defects. The local changes in the atomic arrangements lead to local deformations of the solid and thereby changes of its local mechanical properties. Understanding the mechanisms behind this evolution in the core region of a reactor, and its monitoring or controlling is a critical task in nuclear industry. In this work, using extensive molecular dynamics simulations, we have studied the effects of radiation damage on the local mechanical properties of Zr–$x$Nb alloy. In the first step, the effect of Nb-concentration on the mechanical stability of homogeneous Zr–$x$Nb alloy is investigated. In the second step, we have studied the local changes of the elastic constants due to local changes of the microstructure. These local changes include presence and accumulation of vacancies in the form of dislocation loops or voids, accumulation of Nb atoms in the form of clusters of different morphologies. This study covers both cases of $T=0^{\circ }$K and finite temperatures up to $T=600^{\circ }$K.

The phase transition, elastic and thermodynamic properties of beryllium (Be) have been studied at high pressures by plane-wave ultrasoft pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA). It is found that the hcp → bcc phase transition of Be occurs at 506 GPa (T = 0 K) and occurs at 1200 K (P = 0 GPa). The coefficients of linear thermal expansion of the hexagmal close-packed (hcp), bcc and orthorhombic Be have been calculated. The hcp → orthorhombic → bcc phase transitions do not occur in all range of pressures, that is to say, the orthorhombic Be is not an intermediate phase between the hcp and bcc Be. The obtained bulk modulus (B₀) are 113.2 GPa (for hcp Be), 113.1 GPa (for bcc Be) and 70.5 GPa (for orthorhombic Be), respectively.

By using first principles calculation dependent on the density functional theory (DFT), we have investigated the mechanical, structural properties and the Debye temperature of Fe₂ScM (M=P and As) compounds under various pressures up to 60 GPa. The optical properties have been investigated under zero pressure. Our calculated optimized structural parameters of both the materials are in good agreement with other theoretical predictions. The calculated elastic constants show that Fe₂ScM (M=P and As) compounds are mechanically stable under external pressure below 60 GPa. From the elastic constants, the shear modulus G, the bulk modulus B, Young’s modulus E, anisotropy factor A and Poisson’s ratio $\nu$ are calculated by using the Voigt–Reuss–Hill approximation. The Debye temperature and average sound velocities are also investigated from the obtained elastic constants. The detailed analysis of all optical functions reveals that both compounds are good dielectric material.

Electronic, mechanic and lattice dynamic properties of yttrium-based compounds, X₃Y, where X = Pd, Pt and Rh were investigated using the density functional theory. The electronic band calculations demonstrated that X₃Y compounds are metallic at the cubic crystal structures. The calculated elastic constants using the energy-strain method indicate that the three materials are mechanically stable. The calculated bulk modulus and Young’s modulus values suggest that the Pt₃Y is stiffer than that of the other two. The type of bonding and ductility in the X₃Y compounds were also evaluated based on their B/G ratios, Cauchy pressures (C${}_{12}$–C${}_{44}$) and band structure calculations. These compounds were found to be ductile in nature. The density functional perturbation theory was used to derive full phonon frequencies and total and projected phonon density of states. The computed full phonon spectra for X₃Y compounds show that these compounds in the L1₂ phase are dynamically stable. Debye temperature and specific heat of these compounds were also calculated and evaluated using quasi harmonic approximation.

In this paper, the structural, elastic and phonon properties of Ti₃Al and Y₃Al in L1₂(Cu₃Al) phase are studied by performing first-principles calculations within the generalized gradient approximation. The calculated lattice constants, static bulk moduli, first-order pressure derivative of bulk moduli and elastic constants for both compounds are reported. The phonon dispersion curves along several high-symmetry lines at the Brillouin zone, together with the corresponding phonon density of states, are determined using the first-principles linear-response approach of the density functional perturbation theory. Temperature variations of specific heat in the range of 0–500 K are obtained using the quasi-harmonic model.

${\mathrm{\text{CuGaTe}}}_2$ is a promising thermoelectric (TE) material for high temperature TE applications. This work systematically investigated the structural, elastic and thermodynamic properties of ${\mathrm{\text{Cu}}}_{1-x}{\mathrm{\text{Ag}}}_x{\mathrm{\text{GaTe}}}_2$ ($x$ = 0, 0.25, 0.5, 0.75 and 1) by density functional theory. The calculated lattice volume is expanded with the increase of Ag content, but this expansion is anisotropic. The lattice parameter along $a$-axis is linear expansion, and along $c$-axis is parabolic expansion, which is in good agreement with available experimental data. The phase stability of ${\mathrm{\text{Cu}}}_{1-x}{\mathrm{\text{Ag}}}_x{\mathrm{\text{GaTe}}}_2$ alloy is studied by analyzing the formation energy, cohesive energy and elastic constants. Shear modulus, Young’s modulus, sound velocities, Debye temperature and the minimum thermal conductivity are obtained from the calculated elastic constants. The results show that Ag substitution could reduce the lattice thermal conductivity, which is helpful for improving the TE properties of ${\mathrm{\text{CuGaTe}}}_2$.

This is an ab initio study instituted on the density functional theory (DFT) and the full-potential linearized augmented plane wave (FP-LAPW) calculations that are performed to analyze the mechanical, electronic, optical and thermoelectric properties of the cubic MCoF₃ compound (M = K and Rb). The studied compounds are found thermodynamically and mechanically stable. Moreover, these compounds are found to be elastically anisotropic and ductile. KCoF₃ and RbCoF₃ are classified as half-metallic and anti-ferromagnetic compounds. The optical properties are investigated from the dielectric function for the different energy ranges. The thermoelectric properties such as transport properties are determined as a function of temperature using BoltzTrape code in the range of 20–800 K. The present compounds are found to have p-type character. Also, the majority charge carriers are found to be electrons rather than hole. Useful mechanical, spintronic, optical and thermoelectric applications are predicted based upon the calculations.

The elastic properties of strontium barium niobate single crystals with different strontium content were investigated. The elastic constant and the related hypersonic attenuation showed substantially different values depending on the propagating direction of acoustic waves. This elastic anisotropy was explained based on the uniaxial nature of the order parameter and the diffuse ferroelectric phase transition in this tetragonal system. This observation was correlated with the appearance of strongly polarized central peaks, which reflects strong polarization fluctuations along the uniaxial polar direction.

A gauge-translational Lagrangian approach is developed to describe elastic solid containing static dislocations with finite-sized core. The core self-energy includes the translational part of the general Lagrangian quadratic in torsion and curvature which corresponds to the Riemann–Cartan geometry in three dimensions. In the Hilbert–Einstein case, the gauge equation plays the role of non-conventional incompatibility law. The stress tensor of the modified screw dislocations is smoothed out within the core. The renormalization of the elastic constants caused by the dislocation dipoles is considered. The use of the singularityless dislocation solution modifies the renormalization of the shear modulus in comparison with the case of singular dislocations.