Rabah Khenata - Academia.edu (original) (raw)

Papers by Rabah Khenata

Band-gap engineering of La 1−í µí±¥ Nd í µí±¥ AlO 3 (í µí±¥ = 0, 0.25, 0.50, 0.75, 1) perovskite ... more Band-gap engineering of La 1−í µí±¥ Nd í µí±¥ AlO 3 (í µí±¥ = 0, 0.25, 0.50, 0.75, 1) perovskite using density functional theory: A modified Becke Johnson potential study The structural, electronic, and magnetic properties of the Nd-doped Rare earth aluminate, La 1−x Nd x AlO 3 (x = 0% to 100%) alloys are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The effects of the Nd substitution in LaAlO 3 are studied using the supercell calculations. The computed electronic structure with the modified Becke–Johnson (mBJ) potential based approximation indicates that the La 1−x Nd x AlO 3 alloys may possess half-metallic (HM) behaviors when doped with Nd of a finite density of states at the Fermi level (E F). The direct and indirect band gaps are studied each as a function of x which is the concentration of Nd-doped LaAlO 3. The calculated magnetic moments in the La 1−x Nd x AlO 3 alloys are found to arise mainly from the Nd-4f state. A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at E F. The observed decrease of the band gap with the increase in the concentration of Nd doping in LaAlO 3 is a suitable technique for harnessing useful spintronic and magnetic devices.

In this paper, the structural, electronic and magnetic properties of Nd-doped rare earth aluminat... more In this paper, the structural, electronic and magnetic properties of Nd-doped rare earth aluminate, La 1−x NdxAlO 3 (x = 0%–100%) is studied using the first-principles full potential linearized augmented plane wave (FP-LAPW) method. The effects of partial Nd substitution for La in LaAlO 3 are studied using supercell calculations. The electronic structure analysis indicates La 1−x NdxAlO 3 to be a probable half metal within the spin polarized generalized gradient approximation (GGA). The direct and indirect band gaps are reported and were analyzed as a function of concentration of Nd doping on LaAlO 3. The calculated magnetic moments in La 1−x NdxAlO 3 were found to arise mainly from the Nd-4f electrons which manifest the magnetic nature of the system. The significant band gap narrowing with increase in doping concentration may find important applications in optoelectronic devices.

First-principles investigations of Mn doped zinc-blende ZnO based magnetic semiconductors: Materials for spintronic applications

Materials Science in Semiconductor Processing, 2015

First principle calculations are carried out to study the effect of pressure (up to 30 GPa) on ph... more First principle calculations are carried out to study the effect of pressure (up to 30 GPa) on physical properties of HgIn 2 S 4 and ZnIn 2 S 4 thiospinels. A number of structural, electronic and optical parameters are calculated, and equations are developed for their prediction at different pressures. Highly effective all electron FP-LAPW+lo method coupled with two different approximations (GGA+U and mBJ-GGA) provides very accurate results. All relationships developed between pressure and structural parameters are in full accordance with the established theory thus validating the approach used in the current study. Computed In-S bond length for ZnIn 2 S 4 matches closely with the experimental value. The band gap values of 0.920 eV (1.851 eV) and 1.68 eV (2.733 eV) are obtained with GGA+U (mBJ-GGA) at 0 GPa for HgIn 2 S 4 and ZnIn 2 S 4 , respectively. Additionally, we have calculated the optical properties, namely, the complex dielectric function, refractive index, extinction coefficient, reflectivity, optical conductivity, absorption coefficient and electron energy loss function under pressure effect for radiation up to 30.0 eV. The first critical point also known as optical's absorption edge calculated with GGA+U (mBJ-GGA) appears at 0.939 eV (1.891 eV) and 1.701 eV (2.981 eV) for HgIn 2 S 4 and ZnIn 2 S 4 , respectively. Variation of the absorption spectrum indicates the prospective use of both compounds for device applications, which can be operated on a wide range of the energy scale. The entire work gives useful results of fundamental importance, which can be utilized for the fabrication of optoelectronic devices.

The full-potential linearized augmented plane-wave plus local orbitals method with the generalize... more The full-potential linearized augmented plane-wave plus local orbitals method with the generalized gradient approximation for the exchange–correlation potential (FP-APW + lo-GGA) is used to predict the structural, elastic and high pressure properties of YX with X = S, Se and Te. Ground state properties such as lattice constant, bulk modulus and its pressure derivative are obtained. The pressures at which these compounds undergo structural phase transition from NaCl-type to CsCl-type phases are calculated. The elastic constants and their pressure dependence are calculated using the total energy variation with strain technique. The shear modulus, Young's modulus, Poisson's ratio and Lamé's coefficients are estimated in framework of Voigt–Reuss–Hill approximation for polycrystalline YX aggregates. The Debye temperature is estimated from the average sound velocity. To our knowledge this is the first quantitative theoretical prediction of the elastic and high pressure properties for these compounds and still awaits experimental confirmations.

Keywords: III-P compounds FP-APW + lo Elastic moduli Pressure effect a b s t r a c t The effect o... more Keywords: III-P compounds FP-APW + lo Elastic moduli Pressure effect a b s t r a c t The effect of high-pressures on the structural and elastic properties of XP zinc-blende compounds, with X = B, Al, Ga and In, has been investigated using the full-potential augmented plane wave plus local orbi-tals method within density functional theory. The bulk properties, including lattice constant, bulk mod-ulus and its pressure derivative are obtained. The elastic constants and their pressure dependence are calculated using total energy variation with strain technique. We derived the bulk modulus, shear mod-ulus, Young's modulus and Poisson's ratio for ideal polycrystalline XP aggregates. We estimated the Debye temperature of XP compounds from the average sound velocity. Our results are in reasonable agreement with the available theoretical and experimental data.

Journal of Magnetism and Magnetic Materials, 2011

We have investigated the structural, electronic and magnetic properties of the diluted magnetic s... more We have investigated the structural, electronic and magnetic properties of the diluted magnetic semiconductor (DMS) Cd 1 À x Mn x Te (for x ¼ 0.75 and 1.0) in the zinc blende (B3) phase by employing the ab-initio method. Calculations were performed by using the full potential linearized augmented plane wave plus local orbitals (FP-L/APW+ lo) method within the frame work of spin-polarized density functional theory (SP-DFT). The electronic exchange-correlation energy is described by generalized gradient approximation (GGA). We have calculated the lattice parameters, bulk modulii and the first pressure derivatives of the bulk modulii, spin-polarized band structures, and total and local densities of states. We estimated the spin-exchange splitting energies D x (d) and D x (pd) produced by the Mn3d states, and we found that the effective potential for the minority spin is more attractive than that of the majority spin. We determine the s-d exchange constant N 0 a (conduction band) and p-d exchange constant N 0 b (valence band) and these somewhat agree with a typical magneto-optical experiment. The value of calculated magnetic moment per Mn impurity atom is found to be 4.08 m B for Cd 0.25 Mn 0.75 Te and 4.09 m B for Cd 0.0 Mn 1.0 Te. Moreover, we found that p-d hybridization reduces the local magnetic moment of Mn from its free space charge value of 5.0 m B and produces small local magnetic moments on the nonmagnetic Cd and Te sites.

Canadian Journal of Physics, 2014

Physica Scripta, 2011

The influence of pressure on the structural, elastic, thermal and bonding properties of four pero... more The influence of pressure on the structural, elastic, thermal and bonding properties of four perovskite-type oxides AMO 3 is studied from the point of view of the quantum theory of atoms in molecules. Ab initio investigations are performed by means of the full-potential linear augmented plane-wave method as implemented in the wien2k code. The integrated basin charges resulting from the topological analysis of electronic density provide a partition of the bulk modulus and compressibility into atomic contributions. Special attention is paid to the nonlinear behaviour of the local bonding properties. PACS numbers: 71.15.Mb, 71.15.−m, 62.20.de, 31.15.ae (Some figures in this article are in colour only in the electronic version.)

International Journal of Modern Physics B, 2013

Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg 2 O ... more Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg 2 O 4 (X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B ′ and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (Γ − Γ) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ε(ω), reflectivity R(ω) and energy loss function L(ω), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.

Physica B: Condensed Matter, 2012

The chemical bonding of the ZnAl 2 Se 4 , CdAl 2 Se 4 and HgAl 2 Se 4 defect chalcopyrites has be... more The chemical bonding of the ZnAl 2 Se 4 , CdAl 2 Se 4 and HgAl 2 Se 4 defect chalcopyrites has been studied in the framework of the quantum theory of atoms in molecules (AIM). The GW quasi-particle approximation is used to correct the DFT-underestimation of energy gap, and as a consequence the linear and nonlinear optical properties are significantly enhanced. The second harmonic generation (SHG) displays certain dependence with the ionicity degree decrease through the dependency of the SHG on the band gap. The occurrence of the AIM saddle point is characterized and some clarifying features in relationship with the density topology are exposed, which enable to understand the relation with the second harmonic generation effect.

physica status solidi (b), 2011

We report results of first-principles density functional calculations using the full-potential li... more We report results of first-principles density functional calculations using the full-potential linearized augmented plane wave method. The generalized gradient approximation (GGA) and the Engel-Vosko-GGA (EV-GGA) formalism were used for the exchange-correlation energy to calculate the structural, electronic, linear, and nonlinear optical properties of the chalcopyrite ZnCdTe 2 compound. The valence band maximum and the conduction band minimum are located at the G-point, resulting in a direct band gap of about 0.71 eV for GGA and 1.29 eV for EV-GGA. The results of bulk properties, such as lattice parameters (a, c, and u), bulk modulus B, and its pressure derivative B 0 are evaluated. The optical properties of this compound, namely the real and the imaginary parts of the dielectric function, reflectivity, and refractive index, show a considerable anisotropy as a consequence ZnCdTe 2 posseses a strong birefringence. In addition, the extinction coefficient, the electron energy loss function, and the nonlinear susceptibility are calculated and their spectra are analyzed.

Structural, electronic, and optical properties of ZnO 1− x Se x alloys using first-principles calculations

Chinese Physics B, 2013

Physica B: Condensed Matter, 2010

Full-potential linearized augmented plane waves (FPLAPW) calculations have been used to determine... more Full-potential linearized augmented plane waves (FPLAPW) calculations have been used to determine the equilibrium properties and elastic constants of the chalcopyrite phase of AgGaSe 2 . The topological analysis of the electron density shows a clear polar bonding, with the integrated basin charges revealing a clear dominance of the covalent over the ionic character. The bonding analysis also provides a partition of the bulk modulus and compressibility into atomic contributions. Se is seen to dominate the global behavior (B ¼51.2 GPa), with a local bulk modulus intermediate between the values of the other two atoms: 44.8 (Ga), 51.1 (Se), and 56.6 GPa (Ag).

Computational Materials Science, 2006

We present ab initio calculations for CaS, CaSe and CaTe, in the B1 (NaCl) and B2 (CsCl) phase, b... more We present ab initio calculations for CaS, CaSe and CaTe, in the B1 (NaCl) and B2 (CsCl) phase, by means of accurate first principle total energy calculations using the all-electron full-potential linear muffin-tin orbital method FP-LMTO .The calculations are presented within the local density approximation (LDA).Results are given for structural, electronic and elastic. Good agreement is found with experimental data. The efficiency and the accuracy of this method are so appreciated to predict some properties of this kind of materials