H. Labrim

Hydrogen storage of Mg1?xMxH2 (M = Ti, V, Fe) studied using first-principles calculations

In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg1−x Mx H2 (M = Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa—Kohn—Rostoker (KKR) calculation with the coherent potential approximation (CPA). In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the materials stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.

First principle calculations for improving desorption temperature in Mg16H32 doped with Ca, Sr and Ba elements

Using ab initio calculations, we predict the improvement of the desorption temperature and the hydrogen storage properties of doped Mg-based hydrides such as, Mg15AMH32 (AM = Ca, Sr and Ba) as a super cell 2 × 2 × 2 of MgH2. In particular, the electronic structure has been obtained numerically using the all-electron full-potential local-orbital minimum-basis scheme FPLO9·00-34. Then, we discuss the formation energy calculations in terms of the material stabilities and the hydrogen storage thermodynamic properties improvements. Among others, we find that the stability and the temperature of desorption decrease without reducing significantly the high storage capacity of hydrogen. Moreover, it has been observed that such a doping procedure does not affect the electronic behavior as seen in MgH2, including the insulator state in contrast with the transition metal hydrides, which modify the electronic structure of pure MgH2.

Understanding ferromagnetism and optical absorption in 3d transition metal-doped cubic ZrO2 with the modified Becke-Johnson exchange-correlation functional

The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr1−xTMxO2 (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO2 and have a high value of energy in Mn-doped ZrO2. However, in Co-doped ZrO2, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical...

Interdistance Effects on Flat and Buckled Silicene Like-bilayers

Using ab intio numerical calculations based on the all-electron full-potential local-orbital minimum-basis scheme FPLO9.00-34, we discuss the interdistance effect on the energy gap of two parallel layers of the silicone systems. The like- bilayer systems we dealt with here are relying on a dynamic monolayer of silicene located at distance d along the normal direction z forming with a static one a (AA) stacking arrangement. In particular, we investigate the effect of the dynamic layer by varying the distance d starting from a distance around the bond length of Van der Waals. More precisely, we consider the flat and two buckled geometries in (AA) arrangements. The flat geometry is associated with the usual (AA) configuration appearing in the pure graphene material. For buckled geometry, we can distinguish two configurations. The first one corresponds to the usual buckled configuration that keeps the same vertical distance between the two layers atoms while the remaining one is obtained by reversing one silicene layer. We show that the band gap can be opened by simply varying the distance, starting around a Van der Waals distance, between two parallel silicene for flat and buckled geometries due to an electronic transition of electrons living in pz orbital states. Furthermore, we study the stability between the buckled and the flat configuration in the mono and bilayer system.

New statistical lattice model with double honeycomb symmetry

Inspired from the connection between Lie symmetries and two-dimensional materials, we propose a new statistical lattice model based on a double hexagonal structure appearing in the G2 symmetry. We first construct an Ising-1/2 model, with spin values σ = ±1, exhibiting such a symmetry. The corresponding ground state shows the ferromagnetic, the antiferromagnetic, the partial ferrimagnetic and the topological ferrimagnetic phases depending on the exchange couplings. Then, we examine the phase diagrams and the magnetization using the mean field approximation (MFA). Among others, it has been suggested that the present model could be localized between systems involving the triangular and the single hexagonal lattice geometries.

ELECTRONIC STRUCTURE OF GRAPHENE AND GERMANENE BASED ON DOUBLE HEXAGONAL STRUCTURE

In this paper, we study the electronic structure of monolayer materials based on a double hexagonal geometry with (1×1) and superstructures. Inspired from the two-dimensional root system of an exceptional Lie algebra called G2, this hexagonal atomic configuration involves two hexagons of unequal side length at angle 30°. The principal unit hexagonal cell contains twelve atoms instead of the usual configuration involving only six ones relying only on the (1×1) superstructure. Using ab initio calculations based on FPLO9.00-34 code, we investigate numerically the graphene and the germanene with the double hexagonal geometry. In particular, we find that the usual electronic properties and the lattice parameters of such materials are modified. More precisely, the lattice parameters are increased. It has been shown that, in the single hexagonal geometry, the grapheme and the germanene behave as a gapless semiconductor and a semi-metallic, respectively. In double hexagonal geometry however, both materials becomes metallic.

Wetting and layering transitions in a nano-dendrimer PAMAM structure: Monte Carlo study

This study is based on a nano-model of the dendrimer polyamidoamine (PAMAM). The idea is to examine the magnetic properties of such models in the context of wetting and the layering transitions. The studied system consists of spins Ising ferromagnetic in real nanostructure found in different scientific domains. To study this system, we perform Monte Carlo simulations leading to interesting results recapitulated in two classes. The former is the ground state phase diagrams study. The latter is the magnetic properties at non null temperatures. Also, we analyzed the effect of the terms present in the Hamiltonian governing our system such as the external magnetic field and the exchange couplings interactions.

Magnetic properties of a Lie symmetry double square nanostructure: Monte Carlo study

Abstract Inspired by Lie symmetries and motivated by the existence of the double hexagonal geometry in the two-dimensional material physics, we study a nanosystem based on the double square structure, which we refer as the B2 nanostructure, known as SO(5) Lie algebra. This structure involves two squares of unequal side lengths rotated by angle 45°. The model contains eight atoms instead of four ones appearing in the single square structure. The number of atoms is identified with the non- null roots of the B2 Lie algebra. In particular, we propose a nanolattice model consisting of particles with and S = 1 spins, consisting of two and three states, respectively. Theses spins are placed at the double square sites producing a new geometry formed by and (1×1) structures. More precisely, we study the effect of σ–σ and σ–S coupling exchange interactions. This investigation is made in terms of both external and crystal magnetic fields. First, we elaborate analytically the corresponding ground-state phase diagrams. Second, we investigate the magnetic properties using Monte Carlo method.