Browsing by Author "Akkus, Harun"

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Ab Initio Calculation of Physical Properties of Sodium Chloride
(Amer Scientific Publishers, 2013) Dogan, Emel Kilit; Secuk, Nurullah; Erdinc, Bahattin; Soyalp, Fethi; Akkus, Harun
We have calculated the structural, electronic, optical, dynamical, and thermodynamical properties of sodium chloride crystal using the density functional theory within the generalized gradient approximation. The calculated results for each physical property are presented and compared with available experimental data and previous theoretical data. There are controversial reports in the literature on the electronic band structure of sodium chloride. We especially present data and comments about this controversial subject.
Ab-Initio Calculations of Physical Properties of Alkali Chloride Xcl (X = K, Rb and Li) Under Pressure
(Elsevier, 2015) Erdinc, Bahattin; Secuk, Mehmet Nurullah; Aycibin, Murat; Gulebagan, Sinem Erden; Dogan, Emel Kilit; Akkus, Harun
Structural properties, electronic band structure, real and imaginary parts of complex dielectric function of alkali chloride XCl (K, Rb and Li) compounds were investigated under various pressures using first principles calculations. Moreover, Gibbs free energies were also calculated at those pressures. Calculated results of the Gibbs free energy show that LiCl does not show any structural phase transition. However, structural phase transitions of KCl and RbCl occur from NaCl (B1) to CsCl (B2) at 4.5 and 1.7 GPa pressures, respectively. The electronic band gaps under pressure were also calculated. The calculated physical properties of these compounds are compared with the previous theoretical and experimental results and a good agreement was observed. (c) 2015 The Authors. Published by Elsevier B. V. This is an open access article under the CC BY-NC-ND license.
Ab-Initio Study of Csgecl3 Compound in Paraelectric and Ferroelectric Phases
(Taylor & Francis Ltd, 2016) Erdinc, Bahattin; Secuk, Mehmet Nurullah; Aycibin, Murat; Gulebagan, Sinem Erden; Dogan, Emel Kilit; Akkus, Harun
Structural optimization, electronic energy band structure, density of states, optical, lattice dynamic and thermodynamic properties of CsGeCl3 compound in paraelectric and ferroelectric phases were investigated using the DFT in the GGA and LDA approximations. The obtained results of CsGeCl3 crystal were compared with the available theoretical and experimental results and have been found to be in good agreement with these results.
Ab-Initio Study of the Electronic Structure and Optical Properties of Kno3 in the Ferroelectric Phase
(Iop Publishing Ltd, 2009) Erdinc, Bahattin; Akkus, Harun
The electronic band structure and optical properties of the ferroelectric phase III of KNO3 have been investigated by the first-principle pseudopotential method using the density functional theory under the generalized gradient approximation (GGA) and local density approximation (LDA). The calculated band structure shows that the ferroelectric phase III of KNO3 has a direct band gap with a value of 1.76 eV at the point of the first Brillouin zone (BZ). The structural optimization of KNO3 has been performed using the GGA and LDA. The results of the structure optimization have been compared with the experimental results and have been found to be in good agreement with these results. Moreover, the linear photon-energy-dependent dielectric functions and some optical constants such as energy-loss functions for volume and surface, extinction, reflectivity and absorption coefficients, refractive index and effective number of valance electrons per unit cell participating in the interband transitions have been calculated.
Band Structure and Optical Properties of Antimony-Sulfobromide: Density Functional Calculation
(versita, 2008) Akkus, Harun; Mamedov, Amirullah M.; Kazempour, Ali; Akbarzadeh, Hadi
The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.
Band Structure and Optical Properties of Biocl: Density Functional Calculation
(Gazi Univ, 2012) Koc, Husnu; Akkus, Harun; Mamedov, Amirullah M.
The electronic band structures, density of states (DOS) and optical properties of BiOCl Crystal are investigated using the density functional theory under the local density approximation (LDA). The obtained electronic band structure show that BiOCl crystal has an indirect forbidden band gap of 2.45 eV. The structural optimization for BiOCl has been performed using the LDA. The result of the structure optimization of BiOCl have been compared with the experimental results and have been found to be in good agreement with these results. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated.
Bir Dielektrik Tepki Analizi
(2020) Al-basre, Fayrooz; Akkus, Harun
Bu çalışmada, klasik dispersiyon teorisi çerçevesinde dielektrik spektrumun matematiksel bir analizi yapılmaktadır. Bu analiz, bir kompleks düzlem analizidir. Bu analizle dielektrik fonksiyonun sanal kısmını temel bileşenlerine ayırmak için bir bütüncül analitik yöntem türetilmektedir. Dielektrik fonksiyonun kompleks özelliği kullanılarak bir kompleks düzlem oluşturulmuştur. Bu düzlemde, bir çembere tamamlanan her bir ε_2 (ε_1-1) fonksiyon döngüsü, tek bir Lorentz osilatörü için lineer optik tepkiyi temsil eder. Her bir Lorentz osilatörünün, doğal frekans, enerji ve yarı genişlik gibi parametreleri, bu çemberler analiz edilerek hesaplanır.
Calculation of Electronic Band Structure of Ferroelectric Semiconductor Bismuth Niobium Oxyfluoride (Bi2nbo5f) Crystal
(Gazi Univ, 2014) Erdinc, Bahattin; McCabe, Emma; Duran, Duygu; Secuk, M. Nurullah; Gulebaglan, Sinem Erden; Dogan, Emel Kilit; Akkus, Harun
In this study, the geometric structural optimization, electronic band structure and density of states ( DOS) for electrons of ferroelectric Bi2NbO5F structure with space group Pca21 have been investigated using the density functional theory (DFT) under the local density approximation (LDA). The ground state properties of ferroelectric Bi2NbO5F structure are studied. The computed ground state properties and experimental results are consistent. The energy band structure of Bi2NbO5F compound below T-c shows that it is a ferroelectric semiconductor with narrow band gap of 0.0589 eV. Unfortunately, there is neither experimental nor theoretical electronic band structure study of Bi2NbO5F crystal in the literature, so we could not compare our results.
Comprehensive Theoretical Investigation of Electronic, Structural, Optical, Elastic, and Thermodynamic Properties of Orthorhombic Srta2o6 Compound
(Canadian Science Publishing, 2022) Erzen, Mehmet; Aycibin, Murat; Akkus, Harun
The structural, optical, dynamic, elastic, and thermodynamical properties of orthorhombic SrTa2O6 were computed using density functional theory via two computation codes, namely Wien2k and ABINIT. The findings reveal that SrTa2O6 is a wide bandgap semiconductor with 4.6 eV using the TB-mBJ approximation. The results of bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factors, and Debye's temperature were obtained and discussed in detail. Moreover, The ductile behavior and structural stability mechanism were also explained.
Computation of Physical Properties of Ferroelectric Rbnbo3 Under Pressure
(Taylor & Francis Ltd, 2018) Erzen, Mehmet; Akkus, Harun
The electronic, linear optic and elastic properties of RbNbO3 crystal have been calculated under pressure using the density functional theory for its five different phases, P-1, Pm-3m, P4mm, Amm2 and R3m. It is shown that RbNbO3 crystal electrically exhibits a semiconductor property under zero pressure in these phases except for triclinic phase, P-1, in which the compound has insulator property. Also, the crystal has a direct band gap in the Amm2 phase while it has an indirect band gap in the other four phases. Moreover, the electronic properties were calculated under pressure and it is shown that the locations of top of the valence band and the bottom of the conduction band in the Brillouin Zone were varied with the effect of pressure. The linear optical functions such as dielectric function, refractive index, absorption and extinction coefficients depend on light frequency were calculated under various pressure values for all phases and it is shown that values of the optical constants change with the effect of pressure. Finally, the elastic stiffness tensor of RbNbO3 were calculated for four phases, Pm-3m, P4mm, Amm2 and R3m and the variations of some elastic constants, such as Debye temperature, Poisson ratio, bulk modulus, shear modulus, and Young modulus, with the pressure were investigated.
Density Functional Calculation of the Electronic Structures of Some A5b6c7-Type Crystals
(World Scientific Publ Co Pte Ltd, 2009) Akkus, Harun
The electronic band structures of some A(5)B(6)C(7)-type ternary compounds, BiSeI, BiSI, BiSCl, BiSBr, BiSeBr and SbSeBr, are investigated using the density functional theory and pseudopotential theory under the generalized gradient approximation (GGA). The electronic band structures obtained show that these crystals, except for BiSeI, have an indirect band gap.
A Different Method for Calculation of the Deflection Angle of Light Passing Close To a Massive Object by Fermat's Principle
(Academic Press inc Elsevier Science, 2013) Akkus, Harun
We introduce a method for calculating the amount of deflection angle of light passing close to a massive object. It is based on Fermat's principle. The varying refractive index of medium around the massive object is obtained from the Buckingham pi-theorem. (C) 2013 Elsevier Inc. All rights reserved.
Effect of Pressure on Physical Properties of Luaso4 Crystal
(Iop Publishing Ltd, 2018) Erzen, Mehmet; Akkus, Harun
The physical properties of LuAsO4, such as structural, electronic, linear optical, dynamic, and thermodynamic properties, have been studied under pressure using the density functional theory within the local density approximation. The calculations of electronic band structure of the crystal show that it is an insulator with an indirect band gap value of 4.1977 eV at zero pressure and that the value of band gap increase by increasing pressure. The linear optical properties of the crystal, dependent on the frequency of incoming light, have been calculated. The components of dielectric tensor, static dielectric constant, and refractive index have been calculated under pressure while some optical constants such as energy loss function, extinction coefficient, absorption coefficient, reflectivity, effective dielectric constant, and effective number of valence electrons have been calculated at zero pressure. Moreover, the phonon dispersion, some thermodynamic potentials such as free energy, internal energy, and some thermodynamic properties such as entropy and heat capacity have been calculated under pressure.
Electronic and Optical Properties of Gas: a First-Principles Study
(Gazi Univ, 2010) Erdinc, Bahattin; Akkus, Harun; Goksen, Kadir
The electronic band structure and optical properties of hexagonal GaS are investigated using the density functional theory. The calculated band structure shows that the crystal has an indirect band gap with the value of 1.54 eV in the Brillouin zone at the Gamma -> M. The structural optimization has been performed using the generalized gradient approximation (GGA) and the local density approximation (LDA). The calculated structure optimization of GaS has been compared with the experimental results and has been found to be in good agreement with each other. Furthermore, the linear photon-energy-dependent dielectric functions and some optical constants such as energy-loss functions for volume and surface, extinction, reflectivity and absorption coefficients, refractive index and effective number of valence electrons per unit cell participating in the interband transitions have been calculated.
Electronic and Optical Properties of Γ-Ag3si by Using First Principles
(Korean Physical Soc, 2010) Erdinc, Bahattin; Akkus, Harun
The electronic energy band structure and the optical properties of gamma-Ag3SI are calculated by using density functional theory under the local density approximation (LDA). The calculated electronic band structure shows that gamma-Ag3SI has an indirect gap with a value of 0.46 eV at the M -> Gamma points in the Brillouin zone. A structural optimization has been performed by using the LDA. The optical spectra of the gamma-Ag3SI in the photon range up to 30 eV are calculated by using a first-principles method under the scissor approximation. The real and the imaginary parts of the dielectric function as functions of the photon energy and, thus, the optical constants, such as the energy-loss function, the refractive index, and the effective number of electrons, are investigated. The calculated structural optimization of gamma-Ag3SI is compared with the experimental results and is found to be in good agreement with the experimental data.
Electronic Band Structure and Linear Optical Properties of Paraelectric Kio3
(Iop Publishing Ltd, 2009) Erdinc, Bahattin; Akkus, Harun
The electronic energy band structure, partial (PDOS) and total density of states (DOS), and linear optical properties of the paraelectric KIO3 single crystal are calculated using density functional theory (DFT) in its local density approximation (LDA). The calculated band structure for paraelectric KIO3 indicates that the crystal has a direct bandgap. Using LDA and generalized gradient approximation (GGA), structural optimization has been performed. The optical spectra of the paraelectric KIO3 in the photon energy range up to 30 eV are investigated under the scissor approximation. The real and imaginary parts of the frequency-dependent linear dielectric function, as well as related quantities such as energy-loss function, refractive index and effective number of valence electrons, are calculated. The calculated structural optimization and bandgap of the paraelectric KIO3 have been compared with experimental data and have been found to be in good agreement with the experimental results.
Electronic Structure and Lattice Dynamics of Baceo3 Compound in Cubic Phase
(Springer, 2014) Aycibin, Murat; Erdinc, Bahattin; Akkus, Harun
In this paper, electronic band structure, total density of states, and optical, lattice dynamic and thermo-dynamic properties of BaCeO3 compound in cubic phase were investigated using density functional theory within the generalized gradient approximation. The calculated lattice constant is consistent with the experimental result. In cubic phase, BaCeO3 has a semiconductor character with 2.17 eV band gap.
Exploring Electronic, Structural, Optical, and Elastic Properties of Mgx2o6 (X = Ta, Nb) Compounds for Photovoltaic and Optoelectronic Applications: First Study Effort
(indian Assoc Cultivation Science, 2024) Aycibin, Murat; Celebi, Mustafa; Erzen, Mehmet; Akkus, Harun
In this study, the structural, optical, and elastic properties of tetragonal MgTa2O6 and orthorhombic MgNb2O6 were determined using the Wien2k and ABINIT computational programs with the aid of density functional theory. The results imply that both compounds are classified as wide band gap semiconductor with 4.143 eV (for MgTa2O6) and 3.653 eV (for MgNb2O6) with PBEsol-GGA + TB-mBJ approximation. The findings of bulk modulus, shear modulus, Young modulus, Poisson's ratio, and anisotropy factors were determined and discussed in detail. The ductile behavior and the mechanism of structural stability were also explained.
First Principle Calculation of Electronic Band Structure and Optical Properties of Kio3
(World Scientific Publ Co Pte Ltd, 2009) Akkus, Harun; Erding, Bahattin
The electronic band structure and optical properties of the ferroelectric single crystal KIO3 have been investigated using the density functional methods. The calculated band structure for KIO3 evidences that the crystal has a direct band gap with a value of 2.83 eV. The structural optimization has been performed. The real and imaginary parts of dielectric function, energy-loss function for volume and surface, and refractive index are calculated along the crystallographic axes.
First-Principles Investigation of Structural, Electronic, Optical and Dynamical Properties in Csau
(de Gruyter Open Ltd, 2011) Erdinc, Bahattin; Soyalp, Fethi; Akkus, Harun
The structural, electronic, optical and dynamical properties of CsAu compound in the CsCl(B2) phase were investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated lattice constant, static bulk modulus and first-order pressure derivative of the bulk modulus are reported and compared with previous experimental and theoretical calculations. The calculated electronic band structure for this compound is in good agreement with available theoretical and experimental studies. The present band calculation indicates that CsAu compound has an indirect gap at R -> X points. Furthermore, the linear photon-energy-dependent dielectric functions have been calculated. For the first time, the electronic structure results are used, within the implementation of a linear-response technique, for calculations of phonon properties.