M. KARIMA Belkacem

A theoretical investigation of the structural and electronic properties of rare earth compounds SmX (X = P, Sb, Bi) has been carried out using first-principles calculations within the framework of density functional theory (DFT). The full-potential linearized augmented plane wave (FPLAPW) method was employed, with the exchange– correlation effects treated using the generalized gradient approximation (GGA). To achieve a more accurate description of the electronic structure, the modified Becke–Johnson (mBJ) and Engel–Vosko GGA (EV-GGA) approaches were also applied. The calculated structural parameters show good agreement with available experimental and theoretical results, confirming the reliability of the computational approach. The results indicate that SmP and SmSb are energetically stable in the B1 (NaCl) phase, whereas SmBi is stable in the tetragonal phase. Under high pressure, SmP and SmSb undergo phase transitions from B1 to B2 and tetragonal structures, while SmBi transforms from the tetragonal to the B1 phase. The electronic structure analysis reveals halfmetallic behavior for SmP and SmSb and metallic character for SmBi, with an estimated total magnetic moment of approximately 5 µB.

A theoretical investigation of the structural and electronic properties of rare earth compounds SmX (X = P, Sb, Bi) has been carried out using first-principles calculations within the framework of density functional theory (DFT). The full-potential linearized augmented plane wave (FP-LAPW) method was employed, with the exchange–correlation effects treated using the generalized gradient approximation (GGA). To achieve a more accurate description of the electronic structure, the modified Becke–Johnson (mBJ) and Engel–Vosko GGA (EV-GGA) approaches were also applied. The calculated structural parameters show good agreement with available experimental and theoretical results, confirming the reliability of the computational approach. The results indicate that SmP and SmSb are energetically stable in the B1 (NaCl) phase, whereas SmBi is stable in the tetragonal phase. Under high pressure, SmP and SmSb undergo phase transitions from B1 to B2 and tetragonal structures, while SmBi transforms from the tetragonal to the B1 phase. The electronic structure analysis reveals half-metallic behavior for SmP and SmSb and metallic character for SmBi, with an estimated total magnetic moment of approximately 5 µB.

The effects of structural and chemical disorder on electronic properties
of wurtzite Ga1-x-yInxAlyN quaternary alloys are studied on the basis
of a modified virtual crystal approximation calculated within a simple
tight-binding sp3 with second nearest neighbors. Using a minimal set
of fitting parameters, we show that such an approach provides
analytical results for calculating energy gaps and bowing parameters.
We show that the calculated bowing parameter agrees reasonably well
with experimental data. The essential features of structure and
disorder-induced changes in electronic and optical structure are
exhibited in the sp3 results by two characterization parameters: the
subband energy spacings, and the density of states. The changes in
each of them are found to depend on the interrelated trends of
structure and disorder effects.

THE NEW HALF-METALLIC FERROMAGNETIC QUATERNARY HEUSLER ALLOYS : AN AB INITIO INVESTIGATION

The first-principles approach based on density functional theory (DFT), and the full-potential linearized augmented plane-wave method (FP-LAPW) were employed to investigate the structural, elastic, electronic, and magnetic properties of the NaXNO (X = Ca, Sr, and Ba) quaternary Heusler alloys. The generalized gradient approximation (GGA) as parameterized by Perdew-Burke-Ernzerhof (PBE) and the modified Becke-Johnson exchange potential (mBJ) were used. As far as we know, we present our results which for the first time quantitatively accounts for the electronic structures and magnetic properties of NaXNO (X = Ca, Sr, and Ba) quaternary Heusler alloys. From the total energy calculation using three possible atomic configurations (, , and ), it is found that NaXNO (X = Ca, Sr, and Ba) quaternary Heusler alloys are more stable in the ferromagnetic  phase. From our estimated elastic constants Cij, it is found that all the considered Heusler alloys are mechanically stable in the  phase. The dynamical stability of suggested phases of the considered alloys is thus unknown. Here, we present a theoretical study of the phonon-dispersion relations of one of the considered alloys, the NaCaNO alloy. We show that the  and  phases are dynamically unstable. Out of a set of three phases, the  phase is identified as possible metastable phase based on the analysis of dynamic stability. We have also investigated the robustness of the half-metallicity as a function of the variation of the lattice constant in these alloys. We have found that these alloys are half-metallic ferromagnets (HMF) with a magnetic moment of 2 µB per formula unit at their equilibrium volumes. The spin-polarized electronic band structure and density of states of these quaternary Heusler alloys calculated by GGA (mBJ-GGA) show that the minority spin channels have metallic nature and the majority spin channels have a semiconductor character with a half-metallic gap of 0.49 (2.17), 0.72 (2.28) and 0.96 (2.22) eV for NaCaNO, NaSrCNO, and NaBaNO quaternary Heusler alloys, respectively. Analysis of the density of states and the spin-charge density of these quaternary alloys indicates that their magnetic moments mainly originate from the strong spin-polarization of 2p states of N atoms and O atoms.

Modified Becke-Johnson of the exchange-correlation energy and potentialon the electronics properties ofnitride compounds

Improved first-principles band gaps calculation of groupe III-V nitrides