Browsing by Author "Ugur, G."

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Computational Investigations on Band Structure and Electronic Features of Chromium-Based Carbides and Nitride Cr3px (X = C and N) Through the Fp-Apw Plus Lo Approach
(Academic Press Ltd- Elsevier Science Ltd, 2017) Seddik, T.; Ugur, G.; Soyalp, F.; Khenata, R.; Prakash, Deo; Kityk, I. V.; Verma, K. D.
In this work, we have theoretically investigated the band structure of antiperovskite chromium-based carbides and nitrides Cr3PX (X = C and N) using the first-principles calculation based on the FP-APW+LO method. The principal structural properties i.e., lattice constants (a,b,c) and internal parameters are in accordance with the experimental results. The calculated values of elastic constants indicated that the mechanical strength for both Cr3PC and Cr3PN compounds at (001) plane is higher than the (100) and (010) planes. Moreover, the Cr3PX compounds are expected to be hard materials with ductile nature. In addition, we have found that the FM ground state of herein materials Cr3PC and Cr3PN are energetically favorable with low magnetic moments of about 2.27 and 2.94 AB, respectively, confirming that these are weak ferromagnets. Based on the spin-polarized electronic band structure we have found that both alloys have metallic behavior, such behavior has been shown in the calculated electrical conductivity. We have also estimated other thermoelectric constants like the Seebeck coefficient, thermal conductivity, power factor and electrical resistivity of Cr3PC and Cr3PN compounds. (C) 2016 Published by Elsevier Ltd.
Electronic Structure Calculations of Rare-Earth Intermetallic Compound Yag Using Ab Initio Methods
(Elsevier Science Bv, 2009) Ugur, S.; Ugur, G.; Soyalp, F.; Ellialtioglu, R.
The structural, elastic and electronic properties of YAg-B2(CsCl) were investigated using the first-principles calculations. The energy band structure and the density of states were studied in detail, including partial density of states (PDOS), in order to identify the character of each band. The structural parameters (lattice constant, bulk modulus, pressure derivative of bulk modulus) and elastic constants were also obtained. The results were consistent with the experimental data available in the literature, as well as other theoretical results.
Electronic Structure, Phase Stability, Vibrational and Thermodynamic Properties of the Ternary Nowotny-Juza Materials Limgsb and Liznsb
(Elsevier Science Bv, 2017) Guendouz, Dj.; Charifi, Z.; Baaziz, H.; Soyalp, F.; Ugur, G.; Ugur, S.
A comprehensive study of structure, phase stability, electronic, vibrational and thermodynamic properties of LiMgSb and LiZnSb compounds is performed by carrying out First-principles calculations within densityfunctional theory using the full potential linearized augmented plane wave (FP-LAPW) combined with the pseudo-potential method. The generalized-gradient approximation (GGA) and the local density approximation (LDA) are chosen for the exchange-correlation energy. The Engel-Vosko (EV-GGA) formalism and mBJ approach are applied for the electronic properties. By exchanging the position of the atoms in the cubic structure, three phases (alpha, beta, gamma) are composed. Under ambient conditions, LiMgSb is stable in the cubic a structure however LiZnSb in the wurtzite one. At high pressure, these compounds undergo a structural phase transition from the cubic alpha to cubic gamma phase for LiMgSb and from the wurtzite to cubic gamma phase for LiZnSb, and the transition pressures were calculated. The quasi-harmonic Debye model, in which the phononic effects are predicted, is applied to the investigate of the thermodynamic properties. The temperature effect on the volume V(T), bulk modulus, B(T), thermal expansion coefficient alpha(T), specific heats (C-V and C-p) and Debye temperatures Theta(D), in different pressure and temperature range from 0 to 1000 K are investigated. Our results are in good agreement with previous theoretical calculations and the available experimental data. The band structure, density of states (DOS), and phonon dispersion curves have been obtained and analyzed.
First Principles Study of Hydrogen Storage Material Nabh4 and Lialh4 Compounds: Electronic Structure and Optical Properties
(Iop Publishing Ltd, 2016) Ghellab, T.; Charifi, Z.; Baaziz, H.; Ugur, S.; Ugur, G.; Soyalp, F.
A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out. within density functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation. and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel-Vosko GGA. approach is employed to compute. electronic and optical properties such as reflectivity spectra. The phases a, beta and gamma of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the beta to the. high-pressure gamma phase is determined for NaBH4. and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the [BH4](-) ([AlH4](-)) anions and ionic bonding character between [BH4](-) and Na+ for NaBH4, and [AlH4](-) and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.
First-Principles Investigation of Structural, Electronic and Dynamical Properties in Scausn Alloy
(Elsevier Science Bv, 2007) Soyalp, F.; Ugur, S.; Ugur, G.
A theoretical study of structural, electronic and dynamical properties of the ScAuSn is presented by using the density functional theory within the generalized gradient approximation (GGA). The lattice constant of this material is found to be 6.501 angstrom, which compares very well with the experimental value of 6.419 angstrom. We have carried out band structure and density of states calculations for ScAuSn. Then, a linear-response approach to the density-functional theory is used to derive the phonon frequencies and density of states. (c) 2007 Elsevier B.V. All rights reserved.
First-Principles Study of B2-Like Intermetallics Lamg and Ymg
(Elsevier Sci Ltd, 2012) Ugur, S.; Ugur, G.; Soyalp, F.; Ellialtioglu, M. R.
The first-principles total energy calculations using generalized gradient approximation (GGA) and the plane wave pseudopotential method were employed to investigate the structural, elastic, electronic, and phonon properties of LaMg and YMg in the B2 (CsCl) phase. The elastic constants were derived from the stress strain relation. Lattice parameters, bulk modulus and its pressure derivative, and second order elastic constants were found to be in excellent agreement with the previous experimental and theoretical data. We also carried out the electronic band structure and the density of states (DOS) calculations for LaMg and YMg. Moreover, a linear-response approach to the density functional theory was used to derive the phonon frequencies and the phonon density of states. The temperature variation of specific heats in the range of 0-400 K were obtained using the quasi-harmonic model. (C) 2011 Elsevier Ltd. All rights reserved.
A First-Principles Study of the Structural, Elastic, Electronic and Phonon Properties of Limgp and Limgas in the Α, Β and Γ Phases
(Elsevier Science Sa, 2013) Soyalp, F.; Ugur, G.; Ugur, S.; Sen, H. C.; Ellialtioglu, M. R.
We have studied the structural, elastic, electronic and phonon properties of LiMgP and LiMgAs in the alpha, beta and gamma phases by employing the plane wave pseudopotential method based on density functional theory, within the local density approximation. Lattice parameters, bulk modulus and its pressure derivative, and second order elastic constants were found in good agreement with the literature data. We found that the gamma phase of these compounds are in metallic nature as opposed to alpha and beta phases. A linear-response approach to density functional theory was used to derive the phonon dispersion and the phonon density of states. The calculated zone-center optical phonon modes for these materials were compared with available experimental and theoretical results. Atomic displacement patterns for LiMgP in alpha phase at Gamma and X symmetry points were presented. (C) 2012 Elsevier B. V. All rights reserved.
Investigation of Electronic Structure and Thermodynamic Properties of Quaternary Li-Containing Chalcogenide Diamond-Like Semiconductors
(Iop Publishing Ltd, 2016) Berarma, K.; Charifi, Z.; Soyalp, F.; Baaziz, H.; Ugur, G.; Ugur, S.
Using first-principles calculations based on density functional theory, the structural, electronic and thermodynamic properties of Li2CdGeS4 and Li2CdSnS4 compounds are investigated. We confirmed that both Li2CdGeS4 and Li2CdSnS4 are diamond-like semiconductors of the wurtzstannite structure type based on that of diamond in terms of tetrahedra volume. All the tetrahedra are almost regular with major distortion from the ideal occurring in the LiS4 tetrahedron, with values for S-Li-S ranging. from 105.69 degrees to 112.84 degrees in the Li2CdGeS4 compound. Furthermore, the Cd-S bond possesses a stronger covalent bonding strength than the Li/Ge-S bonds. In addition, the inter-distances in Li2CdSnS4 show a larger spread than the distances in the Li2CdGeS4 compound. The electronic structures have been calculated to understand the bonding mechanism in quaternary Li-containing chalcogenide diamond-like semiconductors. Our results show that Li2CdGeS4 and Li2CdSnS4 are semiconductors with a direct band gap of 2.79 and 2.42 eV and exhibit mixed ionic-covalent bonding. It is also noted that replacing Ge by Sn leads to a decrease in the band gap; this behavior is explained in terms of bond lengths and electronegativity differences between atoms. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy are calculated and show an optical anisotropy for Li2CdGeS4 and Li2CdSnS4. The static dielectric constant epsilon(1)(0) and static refractive index n(0) decrease when Ge is replaced by Sn. The influence of pressures and temperatures on the thermodynamic properties like the specific heat at constant volume C-v, and at constant pressure C-p, the Debye temperature Theta(D), the entropy S and the Gruneisen parameter gamma have been predicted at enlarged pressure and temperature ranges. The principal aspect from the obtained results is the close similarity of both compounds.
Optoelectronic and Thermoelectric Properties of Zintl Yli3a2 (A = Sb, Bi) Compounds Through Modified Becke-Johnson Potential
(Iop Publishing Ltd, 2016) Seddik, T.; Ugur, G.; Khenata, R.; Ugur, S.; Soyalp, F.; Murtaza, G.; Bin Omran, S.
In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi3X2 (X = Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW + lo) method. The exchange-correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke-Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi3Sb2 compound is semiconducting and has an estimated indirect band gap (Gamma-L) of about 0.036 eV while the ground state of YLi3Bi2 compound is semimetallic. Conversely the LDA/TB-mBJ calculations indicate that both compounds exhibit semiconducting characters and have an indirect band gap (Gamma-L) of about 0.15 eV and 0.081 eV for YLi3Sb and YLi3Bi2 respectively. Additionally, the optical properties reveal strong responses of the herein materials in the energy range between the IR and extreme UV regions. Thermoelectric properties such as thermal conductivity, electrical conductivity, Seebeck coefficient, and thermo power factors are also calculated.
Structural, Electronic and Elastic Properties of Ycu From First Principles
(Elsevier, 2009) Ugur, G.; Civi, M.; Ugur, S.; Soyalp, F.; Ellialtioglu, R.
The structural, electronic and elastic properties of YCu compound in the B2 (CsCl) phase were investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA). The electronic density of states (DOS) obtained in this way accorded well with the results of a recent study utilizing the full-potential linearized augmented plane wave (FLAPW) method. We also found that the density of d-states at the Fermi energy was low. The calculated equilibrium properties such as lattice constant, bulk modulus and its first derivative, and the elastic constants were in good agreement with experimental and theoretical results.
Theory Study of Structural Parameters, Elastic Stiffness, Electronic Structures and Lattice Dynamics of Rbrh3 (R = Sc, Y, La and Lu)
(Elsevier Science Bv, 2012) Bouhemadou, A.; Ugur, G.; Ugur, S.; Soyalp, F.; Khenata, R.; Bin-Omran, S.
Density functional-based method has been used to investigate the systematic trends for structural parameters, elastic stiffness, lattice dynamics and thermal properties of cubic perovskite-type RBRh3 depending on the type of R atoms (R are Sc, Y, La and Lu). The structural parameters, single-crystal elastic constants, directional elastic wave velocities and their pressure dependence are calculated and analyzed in comparison with the available experimental and theoretical data. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio, Lame's coefficients, average sound velocity. Debye temperature and thermal conductivity are predicted in the frame work of the Voigt-Reuss-Hill approximation for the polycrystalline RBRh3. The correlation between the mechanical properties and electronic structures has been discussed. Using the density-functional perturbation theory (DFPT), the phonon properties of RBRh3 (R = Sc, Y and La) are investigated for the first time. (C) 2011 Elsevier B.V. All rights reserved.