Kamel Kassali - Academia.edu (original) (raw)

Papers by Kamel Kassali

High Pressure Research, 2007

ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, B... more ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) with pressure. The ωTO and ωLO have a quadratic form with pressure for all boron compounds. The obtained ε∞ and Z* for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ε∞ and Z* have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.

Materials Chemistry and Physics

Journal of Electronic Materials, 2017

Modern Physics Letters B, 2009

The lattice dynamics of the ternary ZnSe 1-x Te x alloy have been studied using first-principles ... more The lattice dynamics of the ternary ZnSe 1-x Te x alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ω TO and ω LO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.

Solid-State Electronics, 2000

This paper is concerned with the pseudopotential investigation of the electronic band structure a... more This paper is concerned with the pseudopotential investigation of the electronic band structure and its related quantities for zinc-blende Ga 1Àx In x N alloys. Our results for the important direct and indirect band-gap energies, electron eective masses and antisymmetric gaps for GaN and InN agree well with the available experimental data. Attention has also been paid to the eect of alloy disorder on the electronic properties of Ga 1Àx In x N semiconductor alloys. For this purpose, the compositional disorder is added to the virtual crystal approximation as an eective potential. Such correction improves signi®cantly the value of the band-gap bowing parameters in Ga 1Àx In x N alloys. #

Superlattices and Microstructures, 2004

The elastic constants of lattice matched and mismatched Ga 1−x In x N y As 1−y alloys with the zi... more The elastic constants of lattice matched and mismatched Ga 1−x In x N y As 1−y alloys with the zincblende structure have been calculated using a pseudopotential formalism combined with the Harrison bond orbital model. The calculations are generally in satisfactory agreement with the experimental results, which are only available for the binary parent compounds. All elastic constants are predicted to significantly increase when further increasing the nitrogen content or the lattice mismatch.

physica status solidi (b), 2002

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physica status solidi (b), 2001

ABSTRACT We have investigated the mechanical properties and elastic constants of zinc-blende Ga1—... more ABSTRACT We have investigated the mechanical properties and elastic constants of zinc-blende Ga1—xInxN alloys, using the pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model. The agreement between our results and the available experimental and other theoretical data was generally satisfactory. Special attention has been given to the effect of alloy disorder on the studied quantities. For this purpose, the compositional disorder is added to the virtual crystal approximation as an effective potential. It is found that except for the anisotropy factor, the compositional disorder should not be ignored in the calculations of the remaining studied quantities of alloys of interest.

Materials Chemistry and Physics, 2002

Using the empirical pseudo-potential method combined with the improved virtual crystal approximat... more Using the empirical pseudo-potential method combined with the improved virtual crystal approximation where compositional disorder is included as an effective potential, we report on the results of composition and temperature-dependent optical band gaps, of the ZnSe 1−x S x (0 ≤ x ≤ 1) type alloys. The obtained results compare reasonably well with the available experimental data.

Journal of Computational and Theoretical Nanoscience, 2013

ABSTRACT The first-principles calculations based on the density-functional perturbation theory ha... more ABSTRACT The first-principles calculations based on the density-functional perturbation theory have been performed using the local-density approximation to investigate many physical properties of Sil(1-x)Ge(x) alloys. Specifically, the structural (lattice constant, bulk modulus), mechanical (elastic constant, Zener anisotropy factor, Young's modulus, isotropic shear modulus, and Poisson's ratio, sound velocities), dynamical (Debye temperature, internal energy, free energy, entropy and specific heat), and the vibrational properties (phonon dispersion curves) are calculated and compared with the available theoretical and experimental data. The effect of composition of Ge on these properties are studied using the virtual crystal (VC) and the supercell approximations. A good agreement between the calculated and experimental values of the lattice constant, the bulk modulus and elastic constants is obtained. The composition dependence of the optical and acoustic phonon frequencies at at the high-symmetry points Gamma, X and L are found to be non-linear.

High Pressure Research, 2005

ABSTRACT We report first-principles calculation results on the structural and elastic properties ... more ABSTRACT We report first-principles calculation results on the structural and elastic properties of ZnSxSe1−x alloy. The calculations done using density functional theory within the local density approximation and employing the virtual-crystal approximation. It is found that the lattice parameter, the phase transition pressure, and the elastic constants (and their derivative with respect to the pressure) follow a quadratic law in x.

Computational Materials Science, 2009

The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied ... more The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied using firstprinciples calculations. These are done using the density-functional perturbation theory (DFPT) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (x TO and x LO ) and of the acoustical phonon frequencies (x TA and x LA ), the high-frequency dielectric coefficient (e 1 ), the dynamic effective charge (Z * ) and the elastic constants (C 11 , C 12 , C 44 ) as a function of the composition (x). We find that the phonon frequencies as well as the elastic constants follow a quadratic law in x and agree well with the available experimental results. The elastic constant tensors for simple cubic 8-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA and experiments.

Modern Physics Letters B, 2009

ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.

High Pressure Research, 2007

ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, B... more ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) with pressure. The ωTO and ωLO have a quadratic form with pressure for all boron compounds. The obtained ε∞ and Z* for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ε∞ and Z* have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.

Materials Chemistry and Physics

Journal of Electronic Materials, 2017

Modern Physics Letters B, 2009

The lattice dynamics of the ternary ZnSe 1-x Te x alloy have been studied using first-principles ... more The lattice dynamics of the ternary ZnSe 1-x Te x alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ω TO and ω LO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.

Solid-State Electronics, 2000

This paper is concerned with the pseudopotential investigation of the electronic band structure a... more This paper is concerned with the pseudopotential investigation of the electronic band structure and its related quantities for zinc-blende Ga 1Àx In x N alloys. Our results for the important direct and indirect band-gap energies, electron eective masses and antisymmetric gaps for GaN and InN agree well with the available experimental data. Attention has also been paid to the eect of alloy disorder on the electronic properties of Ga 1Àx In x N semiconductor alloys. For this purpose, the compositional disorder is added to the virtual crystal approximation as an eective potential. Such correction improves signi®cantly the value of the band-gap bowing parameters in Ga 1Àx In x N alloys. #

Superlattices and Microstructures, 2004

The elastic constants of lattice matched and mismatched Ga 1−x In x N y As 1−y alloys with the zi... more The elastic constants of lattice matched and mismatched Ga 1−x In x N y As 1−y alloys with the zincblende structure have been calculated using a pseudopotential formalism combined with the Harrison bond orbital model. The calculations are generally in satisfactory agreement with the experimental results, which are only available for the binary parent compounds. All elastic constants are predicted to significantly increase when further increasing the nitrogen content or the lattice mismatch.

physica status solidi (b), 2002

The user has requested enhancement of the downloaded file.

physica status solidi (b), 2001

ABSTRACT We have investigated the mechanical properties and elastic constants of zinc-blende Ga1—... more ABSTRACT We have investigated the mechanical properties and elastic constants of zinc-blende Ga1—xInxN alloys, using the pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model. The agreement between our results and the available experimental and other theoretical data was generally satisfactory. Special attention has been given to the effect of alloy disorder on the studied quantities. For this purpose, the compositional disorder is added to the virtual crystal approximation as an effective potential. It is found that except for the anisotropy factor, the compositional disorder should not be ignored in the calculations of the remaining studied quantities of alloys of interest.

Materials Chemistry and Physics, 2002

Using the empirical pseudo-potential method combined with the improved virtual crystal approximat... more Using the empirical pseudo-potential method combined with the improved virtual crystal approximation where compositional disorder is included as an effective potential, we report on the results of composition and temperature-dependent optical band gaps, of the ZnSe 1−x S x (0 ≤ x ≤ 1) type alloys. The obtained results compare reasonably well with the available experimental data.

Journal of Computational and Theoretical Nanoscience, 2013

ABSTRACT The first-principles calculations based on the density-functional perturbation theory ha... more ABSTRACT The first-principles calculations based on the density-functional perturbation theory have been performed using the local-density approximation to investigate many physical properties of Sil(1-x)Ge(x) alloys. Specifically, the structural (lattice constant, bulk modulus), mechanical (elastic constant, Zener anisotropy factor, Young's modulus, isotropic shear modulus, and Poisson's ratio, sound velocities), dynamical (Debye temperature, internal energy, free energy, entropy and specific heat), and the vibrational properties (phonon dispersion curves) are calculated and compared with the available theoretical and experimental data. The effect of composition of Ge on these properties are studied using the virtual crystal (VC) and the supercell approximations. A good agreement between the calculated and experimental values of the lattice constant, the bulk modulus and elastic constants is obtained. The composition dependence of the optical and acoustic phonon frequencies at at the high-symmetry points Gamma, X and L are found to be non-linear.

High Pressure Research, 2005

ABSTRACT We report first-principles calculation results on the structural and elastic properties ... more ABSTRACT We report first-principles calculation results on the structural and elastic properties of ZnSxSe1−x alloy. The calculations done using density functional theory within the local density approximation and employing the virtual-crystal approximation. It is found that the lattice parameter, the phase transition pressure, and the elastic constants (and their derivative with respect to the pressure) follow a quadratic law in x.

Computational Materials Science, 2009

The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied ... more The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied using firstprinciples calculations. These are done using the density-functional perturbation theory (DFPT) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (x TO and x LO ) and of the acoustical phonon frequencies (x TA and x LA ), the high-frequency dielectric coefficient (e 1 ), the dynamic effective charge (Z * ) and the elastic constants (C 11 , C 12 , C 44 ) as a function of the composition (x). We find that the phonon frequencies as well as the elastic constants follow a quadratic law in x and agree well with the available experimental results. The elastic constant tensors for simple cubic 8-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA and experiments.

Modern Physics Letters B, 2009

ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.