<i>Ab-Initio</i>Self-Consistent Density Functional Theory Description of Rock-Salt Magnesium Selenide (MgSe)

We report results on electronic, transport, and bulk properties of rock-salt magnesium selenide (MgSe), from density functional theory (DFT) calculations. We utilized a local density approximation (LDA) potential and the linear combination of atomic orbitals formalism (LCAO). We followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF), to perform a generalized minimization of the energy, down to the actual ground state of the material. We describe the successive, self-consistent calculations, with augmented basis sets, that are needed for this generalized minimization. Due to the generalized minimization, our results have the full, physical content of DFT, as per the second DFT theorem [AIP Advances, 4, 127104 (2014)]. Our calculated, indirect bandgap of 2.49 eV, for a room temperature lattice constant of 5.460 Å, agrees with experimental findings. We present the ground-state band structure, the related total and partial densities of states, DOS and PDOS, respectively, and electron and hole effective masses for the material. Our calculated bulk modulus of 63.1 GPa is in excellent agreement with the experimental value of 62.8 ± 1.6 GPa. Our predicted equilibrium lattice constant, at zero temperature, is 5.424 Å, with a corresponding indirect bandgap of 2.51 eV. We discuss the reasons for the agreements between our findings and available, corresponding, experimental ones, particularly for the band gap, unlike the previous DFT results obtained with ab-initio LDA or GGA potentials.

First-principles study on the mechanical and thermodynamic properties of MoNbTaTiW

Refractory high-entropy alloys(RHEAs)are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K.In this study,the mechanical properties of MoNbTaTiW RHEA are examined by applying calculations based on first-principles density functional theory(DFT)and using a large unit cell with 100 randomized atoms.The phase calculation of MoNbTaTiW with CALPHAD method shows the existence of a stable body-centered cubic structure at a high temperature and a hexagonal closely packed phase at a low temperature.The predicted phase,shear modulus,Young’s modulus,Poisson’s ratio,and hardness values are consistent with available experimental results.The linear thermal expansion coefficient,vibrational entropy,and vibrational heat capacity of MoNbTaTiW RHEA are investigated in accordance with Debye-Grüneisen theory.These results may provide a basis for future research related to the application of RHEAs.

Predictions of Electronic, Transport, and Structural Properties of Magnesium Sulfide (MgS) in the Rocksalt Structure

We report results from ab-initio, self-consistent density functional theory (DFT) calculations of electronic, transport and bulk properties of rock salt magnesium sulfide (MgS). In the absence of experimental data on these properties, except for the bulk modulus, these results are predictions. Our calculations utilized the Ceperley and Alder local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). The key difference between our computations and other previous ab-initio DFT ones stems from our use of successively larger basis sets, in consecutive, self-consistent calculations, to attain the ground state of the material. We predicted an indirect (&Gamma;-X) band gap of 3.278 eV for a room temperature lattice constant of 5.200&Aring;. We obtained a predicted low temperature indirect (&Gamma;-X) band gap of 3.512 eV, using the equilibrium lattice constant of 5.183&Aring;. We found a theoretical value of 79.76 GPa for the bulk modulus;it agrees very well with the experimental finding of 78 &plusmn;3.7 GPa.