El Haj Hassan
@ul.edu.lb
EDST-PRASE
Lebanese University
Professor Fouad El Haj Hassan received the Ph.D. degree in 2000 in condensed matter Physics, from Metz University, France. He joined Lebanese University-Faculty of sciences (I) in 2001, where he is currently a Professor of Physics and condensed matter. Prof. El Haj Hassan is the director of Platform for research and analysis in Environmental Sciences (PRASE – EDST - UL) since October 2015. Coordinator of the Faculty of sciences 4 - annex Baalbek between 2009 and 2013.
Prof. El Haj Hassan is a holder of a Lebanese Research Chair in computational Physics; he is founder and TPC of several international conferences such as the MEDGREEN-LB 2011, ICM2013 IEEE, ICM2015 IEE and ICM2021 IEE. He is plenary speaker in many international conferences and editor board of "Condensed matter physics" and "the scientific world journal". He is referee for more than 12 international journals. Prof El Haj Hassan published 117 peer reviewed journal papers with about 1917 citations and one book chapter. He
EDUCATION
PhD Material sciences
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Nourhan Barakat, Fouad El Haj Hassan, and Michel Kazan
ASME International
Abstract Houston's method for summing phonon modes in the Brillouin zone is applied to exclude specular transmission of phonon modes of specific symmetries, thus, modifying the Acoustic Mismatch Model when phonon heat flux is incident from a heavier to a lighter medium. The Houston method is also used to impose conservation of the number of phonons in each direction of high-symmetry, thus modifying the detailed balance theorem and the Diffuse Mismatch Model. Based on the assumption that phonons are in equilibrium at the interface and are transmitted specularly or diffusely by two-phonon elastic processes, interpolation between the modified Acoustic Mismatch Model and the modified Diffuse Mismatch Model has led to a general analytical formalism for low-temperature interface thermal conductance. The Debye temperature, the only parameter in the derived formalism, is expressed as a function of temperature by assimilating numerically obtained specific heat values to the Debye expression for specific heat. Previous measurements of the low-temperature thermal conductance of smooth and rough interfaces between dissimilar materials could be reproduced numerically without adjustment of model parameters, demonstrating the importance of modifications to the Acoustic Mismatch Model and the Diffuse Mismatch Model and supporting the hypothesis that anharmonic processes play a minimal role in heat transport across the interfaces studied below room temperature. The formalism developed is used to study the thermal conductance of the interface between silicon and germanium because of the potential of silicon-germanium nanocomposites for thermoelectric applications.
Fatima Safieddine, Fouad El Haj Hassan, and Michel Kazan
Elsevier BV
Joumana Assaf, Rima Assaf, and Fouad El Haj Hassan
Springer Science and Business Media LLC
Farraj Maallawi and Fouad El Haj Hassan
Springer Science and Business Media LLC
In the present work, we include the electrons that penetrate the skin layer by seeing their effects on electrical conductivity and metal impedance in both cases of normal and anomalous skin effects. The τ-approximation is used in order to derive new formulas for the electrical conductivity and surface impedance of the normal metal based on the new form of Boltzmann’s kinetic equation.
Kazem Zhour, José M. Otero-Mato, Fouad El Haj Hassan, Hussein Fahs, Majid Vaezzadeh, E. López-Lago, Luis J. Gallego, and Luis M. Varela
Elsevier BV
Abstract A density functional theory study of the effect of the adsorption of a mixture of potassium salt and an imidazolium-based ionic liquid on the electronic and optical properties of graphene and borophene is performed. This addition leads to a downward shift of the Dirac cone for both structures due to the electron transferred from potassium to the graphene and borophene sheets. The transferred charge to the wall and the binding energy of potassium are bigger than in the case of the adsorption of potassium on pristine graphene. The Bader analysis shows that the presence of potassium makes the charge distributions in graphene and the layers of boron atoms in borophene more homogenous and the electronic distribution in the sheets is consequently less affected by the electromagnetic interaction with the ions in the mixture. Moreover, the results show that the optical properties are altered by the metallic cation, especially at low frequencies where ionic liquid-enhanced 2D plasmons are registered due to the doping of 2D sheets by electrons transferred from the potassium atoms leading to near zero values of the parallel components of the dielectric function and refractive index.
Youssef Berro, Michael Badawi, Fouad El Haj Hassan, Mounir Kassir, and Frederik Tielens
Elsevier BV
Abstract Interpreting the interaction between the amorphous silica surface and water is a key step to understand its physicochemical properties. However, due to the flexibility of the structure and the distribution of types and geometries of the silanols one can obtain a broad range of interaction energies, as was already shown in former studies. This time we were able to investigate the distribution of silanols in relation with the calculated interaction energies, and thus designate those different silanols sites. Different dispersion-correction PBE-D (PBE + D2, D3, D3-BJ, TS, TS-HI, MBD, and FI-MBD) and meta-GGA SCAN methods has been used to quantify the interactions between water and defined silanols sites of the surface. All the methods give similar interaction energies, showing equivalent performances of SCAN and PBE-D methods to describe week interactions in our system. Following various routes, we identified a protocol of calculation in order to compute the interaction energies more accurately, taking into consideration the van der Waals (vdW) forces. Once different silanols are correctly described within the calculation level, it is clear that the geometry and environment determine its chemistry. Furthermore, the possible deformation of the silica surface affected by the water interaction is studied. The quantification of the interaction energies is important in order to correctly scale the results and confront with the experiments. With this information in mind, one can think about synthesis techniques that modify the silanols distribution of the silica surface in a way to tune its hydrophobicity and acidity.
F Annane, H Meradji, S Ghemid, H Bendjeddou, F El Haj Hassan, Vipul Srivastava, and R Khenata
Springer Science and Business Media LLC
In this work, we have investigated the structural, electronic and thermodynamic properties of GaP
$$_{1-x}$$
Sb
$$_{x}$$
and AlP
$$_{1-x}$$
Sb
$$_{x}$$
ternary alloys for a number of ordered structures and compositions in a series of first-principles calculations within the density functional theory, using full potential-linearised augmented plane-wave (FP-LAPW) method, as implemented in the WIEN2k code. The exchange-correlation effect was treated within the generalised gradient approximation (GGA) in the form of GGA-PBEsol to optimise the structure and to compute the ground-state properties. In addition to the GGA, the modified Becke–Johnson (mBJ) potential coupled with the spin-orbit interaction (SOI) was also applied to obtain reliable results for the electronic properties. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap showed almost nonlinear dependence on the composition. The GaP
$$_{1-x}$$
Sb
$$_{x}$$
and AlP
$$_{1-x}$$
Sb
$$_{x}$$
alloys are found to be semiconductors with a positive energy gap for the whole concentration range. The spin-orbit splitting
$$\\Delta _{\\mathrm {SO}}$$
was found to increase with Sb composition with a marginal bowing parameter. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. In addition, the quasiharmonic Debye model was applied to analyse the effect of temperature and pressure on the Debye temperature and heat capacity.
Khulud Habanjar, F. El Haj Hassan, and R. Awad
Elsevier BV
Abstract Co-precipitation and solid-state reaction techniques were used to synthesize BaFe12O19 nanoparticles and (BaFe12O19)x(Bi,Pb)-2223 superconducting samples, with 0.00 ≤ x(wt%) ≤ 1.5, respectively. Hard ferromagnetic BaFe12O19 nanoparticles had hexagonal structure with an average size of 63 nm. The structure of the superconducting samples reveal that the added nanoparticles settled at the grain boundaries without altering the host structure superconductors. The elemental composition of the samples is investigated using proton induced X-ray emission. The superconducting transition temperature (Tc) and the critical current density (Jc) were enhanced up to x = 0.5 wt%. The maximum values of dielectric properties of (BaFe12O19)x(Bi,Pb)-2223 were found at lower frequencies and higher temperatures.
Kazem Zhour, José M. Otero-Mato, Fouad El Haj Hassan, Hussein Fahs, Majid Vaezzadeh, E. López-Lago, Luis J. Gallego, and Luis M. Varela
Elsevier BV
Abstract We present a comparative density functional theory study of the electronic and optical properties of graphene and borophene with an adsorbed ionic liquid. The Dirac cones of these two-dimensional nanostructures are not affected by the presence of the ionic liquid close to these sheets, not even in the borophene one in which a very small charge transfer to the ionic liquid anion is detected. However, Bader analysis and charge density calculations showed that the polarization of the ionic liquid induces a redistribution of the electric charge in both sheets as a consequence of the electromagnetic interaction between the anion and cation of the ionic liquid and the electrons on the two-dimensional materials, the effect being notably stronger in graphene than in borophene. Our calculations reveal that several changes take place in the dielectric constant and electron energy loss spectra, including shifts and damping of plasmon bands, related to electrostatically induced changes in the adsorbent surface electron charge distributions and to plasmon loss channels associated to excitations of electrons in the energy levels of the adsorbed ionic liquid species close to the Fermi level of the surface material. While only minor changes are registered in borophene plasmon spectra and in the IR and visible regions of the graphene spectra, important changes in the graphene ultraviolet C and X-ray spectra are registered due to the existence of IL electronic energy levels close to the Fermi level of graphene that are absent in borophene.
Y. Berro, S. Gueddida, Y. Bouizi, C. Bellouard, El-E. Bendeif, A. Gansmuller, A. Celzard, V. Fierro, D. Ihiawakrim, O. Ersen,et al.
Elsevier BV
HYPOTHESIS
One of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts.
EXPERIMENTS
Herein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio.
FINDINGS
The fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones.
Israa Medlej, Abbass Hamadeh, and Fouad El Haj Hassan
Elsevier BV
Abstract Magnetic skyrmions are topologically quasi-particles offering a wide range of applications ranging from memory to oscillator and neuromorphic elements such as neurons and synapses. However, their trajectory driven by currents exhibits the so-called skyrmion Hall angle that is a limiting factor for the above-mentioned applications. Here, we study the stochastic dynamics of synthetic antiferromagnetic skyrmions driven by the spin-Hall effect in a racetrack memory with bifurcation. We show the limit of their application in programmable logic and a possible direction to use this design as a skyrmion based random bit generator.
H. Rekab-Djabri, Mohamed Drief, Manal M. Abdus Salam, Salah Daoud, F. El Haj Hassan, and S. Louhibi-Fasla
Canadian Science Publishing
In this work, first principle calculations of the structural, electronic, elastic, and optical properties of novel AgBr1–xIx ternary alloys in rock-salt (B1) and zinc-blende (B3) structures are presented. The calculations were performed using the full-potential linear muffin-tin orbital (FP-LMTO) method within the framework of the density functional theory (DFT). The exchange and correlation potentials were treated according to the local density approximation (LDA). The lattice constants for the B1 and B3 phases versus iodide concentration (x) were found to deviate slightly from the linear relationship of Vegard’s law. The calculated electronic properties showed that AgBr1–xIx alloys in the B3 structure have a direct band gap (Γ – Γ) for all concentrations of x, which means that they can be used in long-wavelength optoelectronic applications, while in the B1 structure they have an indirect (Γ – R) band gap. The elastic constants Cij, shear modulus G, Young’s modulus E, Poisson’s ratio ν, index of ductility B/G, sound velocities vt, vl, and vm, and Debye temperature θD were also reported and analyzed. By incorporating the basic optical properties, we discussed the dielectric function, refractive index, optical reflectivity, absorption coefficient, and optical conductivity in terms of incident photon energy up to 13.5 eV. The present results were found to be in good agreement with the available experimental and other theoretical results.
Aicha Bahnes, Mohammed El Amine Monir, Younes Mouchaal, Fouad El Haj Hassan, Zohra Bahnes, and Abdelkarim Bendoukha Reguig
Informa UK Limited
ABSTRACT The spin-polarized structural, electronic and magnetic properties of the Ti-doped zincblende ZnS compound at x = 0.50 (Zn0.50Ti0.50S alloy) have been investigated by employing the first-principles full-potential linearised augmented plane wave with local orbitals (FP-L/APW + lo) method within the frame-work of spin-polarized density functional theory (spin-DFT). For the treating of the structural properties, the electronic exchange and correlation (XC) functional was defined by generalised gradient approximation (GGA), whereas both GGA and GGA + U approximations are applied to treat and to compare the electronic and magnetic properties (U is the Coulomb repulsion energy). It has been confirmed that the ferromagnetic (FM) state of this alloy is found the most stable phase; however, all the equilibrium lattice parameters such as; lattice constant (a0), bulk modulus (B0), and its first-pressure derivative (B′) are computed in all paramagnetic, ferromagnetic and anti-ferromagnetic phases. The calculations of electronic properties unveil the perfect half-metallic character in the tetragonal Zn0.50Ti0.50S system. The computed magnetic properties reveal that the total magnetic moment is mainly originated from the transition element (TM) of Ti. Moreover, we have found that the p-d hybridisation is the paramount responsible for the reduction of the magnetic moment of TM from its free space charge value and for the production of minor magnetic moments on the nonmagnetic Zn and S sites.
Kazem Zhour, Fouad El Haj Hassan, Hussein Fahs, and Majid Vaezzadeh
Elsevier BV
Abstract The adsorption of Potassium atom on graphene doped with Nitride, Boron, and Boron nitride hexagons is studied using DFT with LDA and GGA for both spin and non-spin polarization calculations. The distortion in graphene resulting from Boron nitride doping is unnoticeable; alternatively, pure Boron and Nitrogen hexagons introduce high level of distortion in the layer. Adsorption energy, structural geometry, density of state, band structure, charge density, charge transfer, dipole moment and work function are calculated. For Boron and Nitrogen hexagons-doped graphene, the adsorption energy of Potassium increases dramatically compared to pristine graphene, but in the case of Boron nitride hexagons, calculations show weak adsorption energy of Potassium on the doped sheet. The doping of graphene with Boron nitride opens a small band gap, and the adsorption of Potassium rises the Fermi level above the opened gap leading to the formation of n-type semiconductor. Co-existence of partial covalent bond and ionic bond between Potassium and the doped graphene has been demonstrated. The transfer of charges is calculated in four different methods, one by using Bader analysis and the other three are based on DOS, average charge density difference and electric dipole moment.
Youssef Berro, Saber Gueddida, Sébastien Lebègue, Andreea Pasc, Nadia Canilho, Mounir Kassir, Fouad El Haj Hassan, and Michael Badawi
Elsevier BV
Abstract The upgrading of lignin-derived bio-oils involves a HydroDeOxygenation (HDO) reaction through either the Hydrogenation (Hyd) or the Direct DeOxygenation (DDO) route, the latter limiting hydrogen consumption. Herein, dispersion-corrected DFT has been used to evaluate the adsorption behavior of phenol (as a representative model of bio-oils) and two by-products (water and CO) over various crystalline and amorphous silica surfaces to evaluate their potential selectivity (DDO/Hyd) and efficiency (low inhibiting effect) for HDO processing. Phenol can adsorb through three modes, flat π-interaction, flat O-interaction or perpendicular O-interaction. All crystalline surfaces show a preference for the flat π-interaction, which is expected to promote the Hyd route. Over amorphous surfaces the flat O-interaction dominates, and a very specific and strong interaction (around −120 kJ/mol) was found on SiO2-3.3 and SiO2-2.0 surfaces where the phenol molecule loses its aromaticity, which is very promising for its degradation under catalytic conditions. In addition, this makes those surfaces very efficient to adsorb selectively phenol in presence of water and CO. Remarkably, on all silica surfaces, the interaction energy of CO is nearly negligible, which makes them more attractive for HDO process compared to sulfide catalysts with respect to the inhibiting effect criteria.
S. Rmeid, H. Basma, M. Roumie, F. Elhaj Hassan, and R. Awad
Springer Science and Business Media LLC
The effect of nanosized particles NiO addition on the Vickers microhardness of polycrystalline SmBa2Cu3O7-δ was investigated. Various amounts of nanosized particles NiO (x = 0.00, 0.02, 0.04, 0.08, and 0.12 wt%) were added to SmBa2Cu3O7-δ prepared by the solid-state reaction method. Sample characterizations were carried out using X-ray powder diffraction (XRD), particle induced X-ray emission (PIXE), Rutherford backscattering (RBS), and scanning electron microscopy (SEM). The nanosized particle addition does not influence the orthorhombic structure of SmBa2Cu3O7-δ, whereas it affects the oxygen content δ. The electrical and mechanical properties of (NiO)xSmBa2Cu3O7-δ samples were measured using four-standard probe technique and Vickers microhardness in order to investigate the effect of NiO nanosized particles on superconducting transition temperature and Vickers microhardness number Hv. The Vickers microhardness data were analyzed using Hays and Kendall (HK), elastic plastic deformation (EPD), and modified proportional specimen resistance (MPSR) models. The analysis showed that the MPSR model was found to be the best to describe the behavior of Hv.
A. A. Ahmad, S. Mahmoud, B. Alshafaay, R. Halabi, and F. El Haj Hassan
Springer Science and Business Media LLC
AbstractThe full-potential linearized-augmented plane wave calculations based on density functional theory are performed to study the structural, electronic, optical and thermodynamic properties of scandium chalcogenides ScX (X = S, Se, Te) and their ternary alloys at equilibrium as well as under pressure. The revised Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) is used to calculate the structural properties. The electronic and optical properties are calculated employing the GGA and the modified Becke–Johnson (mBJ) approaches. Moreover, the calculated lattice parameters agree well with the experiment results. The structure NaCl-type (B1) of the scandium chalcogenides undergoes under pressure a structural phase transition to CsCl-type (B2) and ZnS-type (B3). The binary and ternary alloys indicate a metallic behavior using GGA and mBJ scheme. The interband contribution to the optical properties is investigated by calculating the dielectric parameters ε1(ω), ε2(ω) and the index of refraction n(ω). A quasi-harmonic Debye model is applied to calculate the thermal properties.
Mohammed El Amine Monir, Fouad El Haj Hassan, Aicha Bahnes, Hadj Baltach, and Abdelkarim Bendoukha Reguig
Informa UK Limited
ABSTRACT The spin-polarised structural, electronic, and magnetic properties of the chalcopyrite BeTiTe2 compound in tetragonal structure (Be0.50Ti0.50Te) have been studied by employing first-principles full-potential linearised augmented plane wave plus local orbitals (FP-L/APW + lo) method within the density functional theory (DFT) and implemented in WIEN2k code. The exchange and correlation energy are described in two frameworks of GGA (generalised gradient approximation) and GGA + U (U is the Hubbard term). The structural analysis confirms that the ferromagnetic phase of the tetragonal BeTiTe2 compound (Be0.50Ti0.50Te) is energetically more favourable; also different equilibrium lattice parameters, such as lattice constants (a0 and c0), bulk modulus (B0), and its first-pressure derivative (Bʹ) have been evaluated in both paramagnetic and ferromagnetic phases. The electronic results of the tetragonal BeTiTe2 compound show a complete half-metallic behaviour. Moreover, the computed total magnetic moment of this compound is close to 4 μB, confirming its half-metallic ferromagnetic nature.
F Soltani, H Baaziz, Z Charifi, F El Haj Hassan, and B Hamad
Springer Science and Business Media LLC
The structural, electronic, magnetic, thermal and elastic properties of Zn$$_{1-x}$$1-xTM$$_{x}$$xSe (TM $$=$$= Mn, Co and Fe) ternary alloys are investigated at x = 0, 0.25, 0.50, 0.75 and 1.00 in the zincblende (B3) phase. The calculations are performed using all-electron full-potential linearised augmented plane-wave (FP-LAPW) method within the framework of the density functional theory (DFT) and the generalised gradient approximation (GGA). The electronic and magnetic properties were performed using the modified Becke–Johnson potential combined with the GGA correlation (mBJ-GGA). The electronic structures are found to exhibit a semiconducting behaviour for Zn$$_{1-x}$$1-xMn$$_{x}$$xSe and Zn$$_{1-x}$$1-xCo$$_{x}$$xSe and a half-metallic behaviour for Zn$$_{1-x}$$1-xFe$$_{x}$$xSe alloys at all concentrations, while CoSe with $$x = 1.00$$x=1.00 is found to exhibit a metallic behaviour. The calculated magnetic moment per substituted transition metal (TM) Mn, Co and Fe atoms for half-metallic compounds are found to be 2.5, 1.5 and 2 $$\\mu $$μ$$_{\\mathrm{B}}$$B, respectively. The p–d hybridisation between the TM d- and Se p-states reduces the local magnetic moment of Mn, Co and Fe and induces small local magnetic moments on Zn and Se sites. In addition, we discuss the mechanical behaviour of binary and ternary compounds and all compounds studied here are mechanically stable.
Mohammed El Amine Monir, Hadj Baltach, Fouad El Haj Hassan, Aicha Bahnes, and Zohra Bahnes
Springer Science and Business Media LLC
Based on the density functional theory (DFT), the full-potential linearized augmented plane wave with local orbital (FP-L/APW+lo) technique is now employed in this approach to understand the structural, electronic, and magnetic properties of simple cubic oxide perovskite NdGaO3 compound. In all this investigation, the exchange-correlation (XC) energy is selected in the framework of spin-polarized generalized gradient approximation (spin-GGA). The structural analysis unveils that the ferromagnetic (FM) phase is the stable ground state of the cubic NdGaO3 compound, where the equilibrium lattice parameters (lattice constant (a0), bulk modulus (B0), and its first pressure derivative (B′)) are determined in both FM and paramagnetic (PM) phases. The spin-polarized electronic properties (band structure and density of states) of the cubic NdGaO3 oxide perovskite are studied under the platform of equilibrium lattice parameters; this investigation demonstrates the half-metallic behavior of the studied cubic NdGaO3 compound because the spin-up case displays the metallic nature, whereas the semiconducting character is observed in spin-down case. The magnetic properties reveal that the total magnetic moment of the cubic NdGaO3 compound is equal to 3 μB and its contribution is mostly generated by Nd atoms, whereas feeble local magnetic moments are installed in non-magnetic Ga and O sites. Through the electronic and magnetic results, we conclude that the cubic perovskite NdGaO3 compound is classified as a half-metallic ferromagnetic material.
Khulud Habanjar, F El Haj Hassan, and R Awad
IOP Publishing
R. Mahdjoubi, Y. Megdoud, L. Tairi, H. Meradji, Z. Chouahda, S. Ghemid, and F. El Haj Hassan
World Scientific Pub Co Pte Lt
First-principles calculations of the structural, electronic, optical and thermal properties of chalcopyrite CuXTe2 (X[Formula: see text]=[Formula: see text]Al, Ga, In) have been performed within density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method, by employing for the exchange and correlation potential the approximations WC-GGA and mBJ-GGA. The effect of X cations replacement on the structural, electronic band structure, density of states and optical properties were highlighted and explained. Our results are in good agreement with the previous theoretical and experimental data. As far as we know, for the first time we find the effects of temperature and pressure on thermal parameters of CuAlTe2 and CuGaTe2 compounds. Thermal properties are very useful for optimizing crystal growth, and predict photovoltaic applications on extreme thermodynamic conditions.
Juliana Srour, Michael Badawi, Fouad El Haj Hassan, and Andrei Postnikov
AIP Publishing
Equilibrium crystal structures, electron band dispersions, and bandgap values of layered GaSe and InSe semiconductors, each being represented by four polytypes, are studied via first-principles calculations within the density functional theory. A number of practical algorithms to take into account dispersion interactions are tested, from empirical Grimme corrections to many-body dispersion schemes. Due to the utmost technical accuracy achieved in the calculations, nearly degenerate energy-volume curves of different polytypes are resolved, and the conclusions concerning the relative stability of competing polytypes drawn. The predictions are done as for how the equilibrium between different polytypes will be shifted under the effect of hydrostatic pressure. The band structures are inspected under the angle of identifying features specific for different polytypes and with respect to modifications of the band dispersions brought about by the use of modified Becke-Johnson (mBJ) scheme for the exchange-correlation potential. As another way to improve the predictions of bandgaps values, hybrid functional calculations according to the HSE06 scheme are performed for the band structures, and the relation with the mBJ results are discussed. Both methods nicely agree with the experimental results and with state-of-the-art GW calculations. Some discrepancies are identified in cases of close competition between the direct and indirect gap (e.g., in GaSe); moreover, the accurate placement of bands revealing relatively localized states is slightly different according to mBJ and HSE06 schemes.
F. Oumelaz, O. Nemiri, A. Boumaza, S. Ghemid, H. Meradji, S. Bin Omran, F. El Haj Hassan, D. P. Rai, and R. Khenata
Springer Science and Business Media LLC
Abstract
In this theoretical study, we have investigated the structural, phase transition, electronic, thermodynamic and optical properties of GaPxSb1−x ternary alloys. Our calculations are performed with the WIEN2k code based on density functional theory using the full-potential linearized augmented plane wave method. For the electron exchange-correlation potential, a generalized gradient approximation within Wu–Cohen scheme is considered. The recently developed Tran–Blaha modified Becke–Johnson potential has also been used to improve the underestimated band gap. The structural properties, including the lattice constants, the bulk moduli and their pressure derivatives are in very good agreement with the available experimental data and theoretical results. Several structural phase transitions were studied here to establish the stable structure and to predict the phase transition under hydrostatic pressure. The computed transition pressure (Pt) of the material of our interest from the zinc blende (B3) to the rock salt (B1) phase has been determined and found to agree well with the experimental and theoretical data. The calculated band structure shows that GaSb binary compound and the ternary alloys are direct band gap semiconductors. Optical parameters such as the dielectric constants and the refractive indices are calculated and analyzed. The thermodynamic results are also interpreted and analyzed.
Joumana Assaf, F. El Haj Hassan, É.C.M. Nascimento, and Amine Haydar
Elsevier BV
Abstract SA-CASSCF and ic-MRCI methods have been performed to calculate 26 low-lying (2s+1)Λ(±) electronic states located below 40,250 cm−1 for 175Lu1H molecule. The potential energy curves (PECs) for these states are displayed in the range of 1.00–3.50 A. The spectroscopic constants such as R e , T e , ω e and ω e χ e are reported for the first time. Moreover, the permanent and transition electric dipole moments are plotted versus internuclear distance ( R ). Subsequently, for the first 13 (2S+1)Λ(±) states located below 30,000 cm−1, the spin-orbit couplings (SOC) of 30 Ω(±) states are calculated with their spectroscopic constants.