International Journal of Computational Materials Science and Engineering

First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and magnetic properties of NaS, NaSe and NaTe alkali-metal chalcogenides binary compounds. These compounds in different crystalline phases: NaCl (B1), CsCl (B2), ZB (B3), NiAs (B8₁), WZ (B4) and Pnma were calculated within the generalized gradient approximation (GGA-PBE) and the modified Becke–Johnson approach (mBJ-GGA-PBE) for the exchange-correlation energy and potential. We found that the most stable phase for the NaX binary compounds is the nonmagnetic Pnma phase. The calculated lattice parameters, bulk moduli, their first-pressure derivatives and internal parameters are in good agreement with the other theoretical data. The electronic band structure and density of states show that half-metallic and magnetic character arises, which can be attributed to the presence of spin-polarized $p$ orbitals in the group VI elements. The NaS, NaSe and NaTe binary compounds show half-metallic character in ZB and WZ phases, with an integer magnetic moment of 1 ${\mu }_{\mathrm{\text{B}}}$ per formula unit and half-metallic gaps.

In this paper, the free vibration and buckling behaviors of nanoscale beams with different boundary conditions are analyzed using the integral formulation of Eringen’s nonlocal elasticity theory. To this end, both strain- and stress-driven nonlocal integral models are employed. The nanobeams are modeled according to the Euler–Bernoulli beam theory. Moreover, a novel numerical approach is proposed for solving the obtained governing equations. By this numerical method, which uses matrix differential and integral operators, the integral governing equation is directly solved and the difficulties related to converting the integral governing equation into the differential one are bypassed. Comparisons are made between the predictions of strain and stress-driven models about the vibration and buckling responses of nanobeams subject to various end conditions. The results indicate that based on the stress-driven model, the frequency and critical buckling load increase with increasing the nonlocal parameter, whereas they decrease when the strain-driven integral model is used.

The problem of the symmetric and antisymmetric vibrations are attempted for the elastic plate with voids immersed in a liquid. The frequency equations are derived and deduced for the cases of plate wave, flexural and Rayleigh waves. It is also derived the cases when the liquid is replaced by vacuum/air. The two modes of vibration for the modified symmetric, antisymmetric, plate, flexural and Rayleigh waves in the considered medium are discussed. Numerically and analytically, the phase speeds and attenuations of symmetric and antisymmetric vibration, plate wave, flexural and Rayleigh waves are computed for a particular model. The effects of voids parameters on the phase speeds are also discussed.

We have studied the structural, electronic, magnetic, thermoelectric and optical properties of the half-metal BaRuO₃ using the accurate full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The generalized gradient approximation (GGA) was used to treat the exchange and correlation potential. The GGA$+U$ approximation was also used to enhance the description of the electronic structure after calculating theoretically the Coulomb repulsion ($U=7$eV). The ferromagnetic (FM) phase of BaRuO₃ is more stable. This result is in accordance with experimental and theoretical calculations. The calculated magnetic moments in BaRuO₃ were found to arise especially from the Ru-4d state electrons. We have obtained the semiconductor gap (0.9eV) in spin-up while in spin down, the metal character was dominant, and therefore BaRuO₃ has a half-metallic behavior. The thermoelectric efficiency was 0.12 at room temperature. Here we have considered only the electronic thermal conductivity, we have not included the lattice thermal conductivity. The relaxation time was assumed constant. The $\mathrm{\text{GGA}}+U$ approximation was also used to analyze the optical properties by determining the complex dielectric function from which are derived the other parameters.

We present first-principles calculations of the structural, electronic and magnetic properties of Gd-doped ${\mathrm{\text{Al}}}_{0.25}{\mathrm{\text{Ga}}}_{0.75}\mathrm{\text{N}}$ based on the density functional theory within $\mathrm{\text{LSDA}}+U$ schemes. It is found that Gd atom favors substituting for Al site. Compared with undoped ${\mathrm{\text{Al}}}_{0.25}{\mathrm{\text{Ga}}}_{0.75}\mathrm{\text{N}}$, the Gd-doped ${\mathrm{\text{Al}}}_{0.25}{\mathrm{\text{Ga}}}_{0.75}\mathrm{\text{N}}$ has become an indirect band gap semiconductor of reduced band gap. The magnetic moment $7.15{\mu }_B$ per molecule mainly comes from Gd ion with little contribution from the Ga, Al and N atoms. It is confirmed that the ferromagnetic configuration is stable for ${\mathrm{\text{Al}}}_{0.1875}{\mathrm{\text{Gd}}}_{0.0625}{\mathrm{\text{Ga}}}_{0.75}\mathrm{\text{N}}$. It is found also that there is hybridization between the forbital of the Gd atom and the $p$ orbital of the N atom.

In this paper, a semi analytical-numerical technique called differential transform method (DTM) is applied to investigate free vibration of nanobeams based on non-local Euler–Bernoulli beam theory. The essential steps of the DTM application include transforming the governing equations of motion into algebraic equations, solving the transformed equations and then applying a process of inverse transformation to obtain accurate mode frequency. All the steps of the DTM are very straightforward, and the application of the DTM to both the equations of motion and the boundary conditions seems to be very involved computationally. Besides all these, the analysis of the convergence of the results shows that DTM solutions converge fast. In this paper, a detailed investigation has been reported and MATLAB code has been developed to analyze the numerical results for different scaling parameters as well as for four types of boundary conditions. Present results are compared with other available results and are found to be in good agreement.