Mohammed Benali Kanoun

Molecular-dynamics study of the structural, elastic and thermodynamic properties of cadmium telluride

Abstract In this work, structural, elastic and thermodynamic properties of cubic cadmium telluride (c-CdTe) have been investigated by molecular-dynamics (MD) simulation using the well-tested Tersoff potential under pressure and by varying temperature. Fundamental bulk properties, elastic constants, thermal expansion coefficient, heat capacity and Gruneisen parameter have been studied. The structural properties in the rock-salt structure are also studied and compared with other works.

Controlled Surface Segregation Leads to Efficient Coke‐Resistant Nickel/Platinum Bimetallic Catalysts for the Dry Reforming of Methane

Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO‐probe IR spectroscopy, high‐angle annular dark‐field scanning transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, extended X‐ray absorption fine structure analysis, X‐ray absorption near‐edge structure analysis, XRD, and X‐ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island‐modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni‐rich core and a Ni/Pt alloy shell upon thermal treatment. These catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

Ab initio investigation on the magnetic ordering in Gd doped ZnO

The current study investigates the magnetic properties of the Gdx Zn1-xO, with x=0.0625 and 0.0185, doped semiconductor using the full potential (linearized) augmented plane wave plus local orbital method. We show that in contrast to the findings of Shi et al. [J. Appl. Phys. 106, 023910 (2009)], the implementation of the Hubbard U parameter to the Gd f states favors an antiferromagnetic phase in both wurtzite GdO and Gdx Zn1-xO. Spin polarized calculations on Gdx Zn1-xO indicate that, even if a ferromagnetic ground state were favored, the magnetic influence of Gd in a perfect ZnO wurtzite lattice is highly localized and limited to the first three nearest neighboring O atoms. Increasing the supercell size and thus diluting the concentration of Gd within the ZnO matrix does not show any changes in the net magnetic moment between these three O atoms nor in the remaining lattice sites, indicating that sizing effects do not influence the range of matrix polarization. We conclude that the localized Gd induced ...

Ab initio study of structural parameters and gap bowing in zinc-blende AlxGa1−xN and AlxIn1−xN alloys

We present first-principles calculations of the structural and electronic properties of zinc-blende AlxGa1−xN and AlxIn1−xN alloys by application of the all-electron full-potential linearized augmented plane-wave method within density-functional theory and the local-density approximation. When the parameter x varies, both the lattice constant a and the bulk modulus B are found to vary linearly for AlxGa1−xN, while for AlxIn1−xN the lattice parameters show an upward bowing. The calculated band-gap variation for the two alloys varies nonlinearly as a function of composition x, with a strong downward bowing for AlxIn1−xN.

Molecular-dynamics simulations of structural and thermodynamic properties of ZnTe using a three-body potential

A three-body potential (Tersoff potential) coupled with a molecular-dynamics (MD) method have been used to calculate structural and thermodynamic properties of ZnTe in zinc-blende phase. Both of lattice constant and bulk modulus are computed as important ground-state properties, also is determined the cohesive energy. All these properties will be calculated in rock-salt phase where an appropriate adjustment of potential parameters. We extend our investigation to thermodynamic properties, where the lattice thermal expansion, and the specific heat are determined. The elastic properties are also investigated throughout the calculation of elastic constants.

Spin-polarization reversal at the interface between benzene and Fe(100)

The spin-polarization at the interface between Fe(100) and a benzene is investigated theoretically using density functional theory for two positions of the organic molecule: planar and perpendicular with respect to the substrate. The electronic and magnetic properties as well as the spin-polarization close to the Fermi level strongly depend on the benzene position on the iron surface. An inversion of the spin-polarization is induced by p-d hybridization and charge transfer from the iron to the carbon sites in both configurations.

First principle investigations of the physical properties of hydrogen-rich MGH2

Hydrogen being a cleaner energy carrier has increased the importance of hydrogen-containing light metal hydrides, in particular those with large gravimetric hydrogen density like magnesium hydride (MgH 2 ). In this study, density functional and density functional perturbation theories are combined to investigate the structural, elastic, thermodynamic, electronic and optical properties of MgH 2 . Our structural parameters calculated with those proposed by Perdew, Burke and Ernzerof generalized gradient approximation (PBE-GGA) and Wu‐Cohen GGA (WC-GGA) are in agreement with experimental measurements, however the underestimated band gap values calculated using PBE-GGA and WC-GGA were greatly improved with the GGA suggested by Engle and Vosko and the modified Becke‐Johnson exchange correlation potential by Trans and Blaha. As for the thermodynamic properties the specific heat values at low temperatures were found to obey the T 3 rule and at higher temperatures Dulong and Petit’s law. Our analysis of the optical properties of MgH 2 also points to its potential application in optoelectronics.

Structural stability, elastic constants, bonding characteristics and thermal properties of zincblende, rocksalt and fluorite phases in copper nitrides: plane-wave pseudo-potential ab initio calculations

We report plane-wave pseudo-potential ab initio calculations using density functional theory in order to investigate the structural parameters, elastic constants, bonding properties and polycrystalline parameters of copper nitrides in zincblende, rocksalt and fluorite structures. Total and partial densities of states indicate a metallic character of these copper nitrides. We estimate bond strengths and types of atomic bonds using Mulliken charge density population analysis and by calculating the electronic localized function. These results reveal the coexistence of covalent, ionic, and metallic bonding.

Ferromagnetism carried by highly delocalized hybrid states in Sc-doped ZnO thin films

We present first-principles results for Sc-doped ZnO thin films. Neighboring Sc atoms in the surface and/or subsurface layers are found to be coupled ferromagnetically, where only two of the possible configurations induce spin polarization. In the first configuration, the polarization is carried by the Sc d states as expected for transition metal doping. However, there is a second configuration which is energetically favorable. It is governed by polarized hybrid states of the Zn s, O p, and Sc d orbitals. Such highly delocalized states can be an important ingredient for understanding the magnetism of doped ZnO thin films.

Ferromagnetism in Cr-doped passivated AlN nanowires

We apply first principles calculations to predict the effect of Cr doping on the electronic and magnetic properties of passivated AlN nanowires. We compare the energetics of the possible dopant sites and demonstrate the favorable configuration ferromagnetic ordering. The charge density of the pristine passivated AlN nanowires is used to elucidate the bonding character. Spin density maps demonstrate an induced spin polarization for N atoms next to dopant atoms, though most of the magnetism is carried by the Cr atoms. Cr-doped AlN nanowires turn out to be interesting for spintronic devices.