Yazar "Parlak, Cihan" seçeneğine göre listele

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    Ab initio calculations on electronic and lattice dynamical properties of CuInSe2 and CuInS2
    (Bolu Abant İzzet Baysal Üniversitesi, 2002) Parlak, Cihan; Eryiğit, Resul
    ÖZET CuInSe2 ve CuInS2'ün Elektronik ve Örgü Dinamiği Özellikleri Üzerine Ab initio Hesaplamalar Cihan Parlak Yüksek Lisans, Fizik Bölümü Tez Danışmanı: Yrd. Doç. Dr. Resul Eryiğit Temmuz 2002, 68 sayfa Bu tezde chalcopyrite yarı iletkenler CuInSe2 ve CuInS2 'ün yapısal, dinamik, dielektirik ve elektronik özelliklerini inceledik. Öncelikle hesaplarda yerel yoğunluk yaklaşımı, norm-korunumlu pseudopotential ve düzlem dalga tabanı kullanıldı. Elekronik band yapıları iki madde içinde benzer bulundu. Born etkin yük tensörleri, dielektirik geçirgenlik tensörleri, Brillouin bölgesi merkezindeki fonon frekansları ve mod titreşim güçleri hesaplandı. Bu değerler literatürdeki değerlerle karşılaştırılarak bazı verilerle uyumlu olduğu görüldü. Anahtar Kelimeler: Chalcopyrite yarıiletkenler, elektronik band yapıları, Born ektin yük tensörleri, fonon frekansları, dilektrik geçirgenlik tensörleri.
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    Ab initio Hartree-Fock and density functional theory study on characterization of 3-(5-methylthiazol-2-yldiazenyl)-2-phenyl-1H-indole
    (Pergamon-Elsevier Science Ltd, 2010) Büyükuslu, Halim; Akdoğan, Mustafa; Yıldırım, Gürcan; Parlak, Cihan
    The optimized molecular structures, vibrational frequencies, corresponding vibrational assignments, thermodynamic properties, UV-vis spectra and atomic charges of 3-(5-methylthiazol-2-yldiazeny1)-2-phenyl-1H-indole molecule have been investigated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods at 6-31G (d,p) basis set. The obtained bond lengths and bond angles have been seen to be good agreement with the experimental data. After calculated vibrational frequencies have been compared with each other, the correlation coefficient has been determined. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and energy band gap. Infrared intensities and Raman activities have been also reported. (C) 2010 Elsevier B.V. All rights reserved.
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    Ab initio pressure-dependent vibrational and dielectric properties of chalcopyrite CuAlS2
    (Amer Physical Soc, 2004) Parlak, Cihan; Eryiğit, Resul
    We have performed an ab initio study of pressure-dependent lattice dynamical properties of chalcopyrite semiconductor CuAlS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center, and their Gruneisen parameters are calculated using density functional perturbation theory. We compare the Gruneisen parameters of the calculated quantities with those of zinc-blende type materials and found similar trends.
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    Ab initio vibrational and dielectric properties of chalcopyrite CuInS2
    (Springer, 2003) Eryiğit, Recep; Parlak, Cihan; Eryiğit, Resul
    We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor CuInS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties agree with infrared and Raman measurements.
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    Ab initio vibrational and dielectric properties of the chalcopyrite CuInSe2
    (Amer Physical Soc, 2002) Parlak, Cihan; Eryiğit, Resul
    We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor CuInSe2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center, and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties agree with some of the infrared, Raman, and neutron measurements.
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    Ab initio vibrational and dielectric properties of the chalcopyrite CuInSe2
    (American Physical Society, 2002) Parlak, Cihan; Eryi?it, Resul
    We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor CuInSe2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center, and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties agree with some of the infrared, Raman, and neutron measurements.
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    Ab initio volume-dependent elastic and lattice dynamical properties of chalcopyrite CuGaSe2
    (Amer Physical Soc, 2006) Parlak, Cihan; Eryiğit, Resul
    We report the results of a first principles study of volume-dependent elastic and lattice dynamical properties of chalcopyrite semiconductor CuGaSe2. The calculations have been carried out within density-functional perturbation theory framework, employing the local density functional approximation with norm-conserving pseudopotentials and a plane-wave basis set. Born effective charge tensors, dielectric permittivity tensors, the phonon frequencies at the Brillouin zone center and their Gruneisen parameters are calculated by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. We compared the Gruneisen parameters of the calculated quantities to those of ZnSe which is the isoelectronic analog of CuGaSe2 and other zinc-blende-type materials and found similar trends.
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    Density functional theory study on the identification of 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol
    (Pergamon-Elsevier Science Ltd, 2011) Parlak, Cihan; Akdoğan, Mustafa; Yıldırım, Gürcan; Karagöz, Nurettin; Budak, Erhan; Terzioğlu, Cabir
    This study deals with the identification of a title compound, 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol by means of quantum chemical calculations. The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments, thermodynamic properties, charge analyses, nuclear magnetic resonance (NMR) chemical shifts and ultraviolet-visible (UV-vis) spectra of the title molecule in the ground state were evaluated using density functional theory (OFT) with the standard B3LYP/6-311++G(d,p) method and basis set combination for the first time. Theoretical vibrational spectra of the title compound were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the obtained optimized geometric parameters (bond lengths, bond angles and bond dihedrals) and vibrational frequencies were observed to be in good agreement with the available experimental results. Moreover, the calculations of the electronic spectra, C-13 and H-1 chemical shifts were compared with the experimental ones. Furthermore, we not only simulated the frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also determined the transition states and energy band gaps, as well. It was found that charge analyses supported the evidences of MEP. Infrared intensities and Raman activities were also reported. (C) 2011 Elsevier B.V. All rights reserved.
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    Elastic, electronic, lattice dynamical properties and electron-phonon interaction in the ternary superconductors Ba(GaGe) and Ba(GaSi)
    (Elsevier Science Bv, 2015) Parlak, Cihan
    We report the results of an ab-initio study of electronic, and detailed lattice dynamical properties of superconducting materials, Ba(GaGe) and Ba(GaSi). The phonon dispersion curves along the high-symmetry directions and phonon frequencies parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The band structure, and partial densities of states and Fermi surface topology are also discussed. The transition temperature T-c of superconductivity in these compounds have been evaluated. We found the values of electron-phonon coupling constant at 0.85 and 0.84 for Ba(GaSi) and Ba(GaSe). (C) 2014 Elsevier B. V. All rights reserved.
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    Elastic, electronic, lattice dynamical properties and electron-phonon interaction in the ternary superconductors Sr(GaGe) and Sr(GaSi) at high pressure
    (Elsevier, 2017) Parlak, Cihan
    We report the results of an ab - initio study of electronic, and detailed lattice dynamical properties of superconducting materials, Sr(GaGe) and Sr(GaSi) under high pressure. The phonon dispersion curves along the high-symmetry directions and phonon frequencies parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The Vickers hardness belonging to the compounds is also evaluated clearly. Moreover the band structures, partial densities of states and Fermi surface topologies are discussed in detail. At the same time we advance in-depth understanding of the relationship between the properties determined and superconducting characteristic. The transition temperatures for the compounds have been detected. We find the values of electron-phonon coupling constant as 0.99 and 0.92 for Sr(GaSi) and Sr(GaGe), respectively.
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    Electronic and pressure dependent vibrational properties of silicide Sr(Ni0.5Si0.5)(2)
    (Elsevier Science Bv, 2012) Parlak, Cihan
    We report a detailed ab initio study of the structural, electronic, and volume dependent elastic and lattice dynamical properties of Sr(Ni0.5Si0.5)(2). The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. The phonon dispersion curves along the high-symmetry directions and phonon frequencies with their Gruneisen parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The band structure, and partial densities of states and Fermi surface topology are also discussed. (C) 2012 Elsevier B.V. All rights reserved.
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    Electronic band structure and volume-dependent lattice dynamical properties of superconductor Sr (AlGe)
    (Elsevier Science Bv, 2014) Parlak, Cihan
    Ternary germanide Sr (AlGe) is a superconductor at 6.7 K. We report the results of an ab initio study of electronic, and detailed lattice dynamical properties of superconducting material. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. The vibrational properties and the electron-phonon calculations are represented using density functional perturbation theory. (C) 2014 Elsevier B.V. All rights reserved.
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    Experimental and theoretical studies on the identification of p-biphenyloxycarbonylphenyl acrylate
    (Pergamon-Elsevier Science Ltd, 2011) Çetin, Sedat; Yıldırım, Gürcan; Parlak, Cihan; Akdoğan, Mustafa; Terzioğlu, Cabir
    This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet-visible (UV-vis) spectra were analyzed utilizing ab initio Hartree-Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly. (C) 2011 Elsevier B.V. All rights reserved.
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    First principles investigation of lattice dynamical properties of Cu-based chalcopyrite semiconductors and high dielectric constant materials
    (Bolu Abant İzzet Baysal Üniversitesi, 2008) Parlak, Cihan; Eryiğit, Resul
    Bakır tabanlı üçlü yarıiletkenlerin yapısal, elastik ve örgü dinamiği özelliklerinin basınca bağımlılığı ve çok yüksek genişlikte düşük frekans dielektrik sabitli bazı perovskite yapıların elektronik, yapısal ve dielektrik özelliklerinin temel ilkelerden incelenmesi olarak iki konu çalışmayı planlamıştık.Öncelikle kalkopirit yarı iletkenler CuGaSe2 and CuAlS2'nin hacime bağlı elastik ve örgü dinamiği özellikleri üzerine ab initio hesaplamalar yaptık. Hesaplamalar yerel yoğunluk yaklaşımı çerçevesinde norm korunumlu sanal potansiyeller ve düzlem dalga tabanı kullanılarak gerçekleştirilmiştir. Born etkin yük tensörleri, dielektrik geçirgenlik tensörleri, Brillouin bölge merkezli fonon frekansları ile bunların grüneissen parametreleri, yoğunluk fonksiyonel tedirginme teorisi kullanılarak hesaplandı. Hesaplanan büyüklüklerin grüneissen parametreleri çinkoblende türü yapıların ki ile aynı biçimde olduğu bulundu. Ayrıca hesaplanan elastik-sertlik katsayılarının sanal kübik davranış gösterdiği tespit edildi.Ikinci araştırma konusu olarak, yüksek dielektrik sabitli perovskite türevi oksit Na1/2Bi1/2Cu3Ti4O12 malzemesinin elektronik, dielektrik ve örgü dinamiği özelliklerinin ab initio sonuçlarını rapor ettik. Hesaplamalar yerel spin yoğunluk yaklaşımı, norm korunumlu sanal potansiyeller ve düzlem dalga tabanı kullanılarak yapıldı. Taban durumu direk bant aralıklı antiferromanyetik yarıiletken olarak bulundu. Born etkin yük tensörleri, dielektrik geçirgenlik tensörleri ve Brillouin bölge merkezli fonon frekansları gibi örgü dinamiği özellikleri yerel yoğunluk tedirginme teorisi ile hesaplanarak, daha önce sıklıkla çalışılan CaCu3Ti4O12 ve CdCu3Ti4O12 malzemelerine benzerlik gösterdiği tespit edildi. Hesaplanan elektronik (?o=11.5) ve statik (??=150) dielektrik katsayıları, gözlenen yüksek dielektrik katsayılarının dışsal nedenli olduğunu göstermiştir. Statik dielektrik sabitine temel katkı düşük frekanslı (50 1/cm) yüksek mod etkin yüke sahip kızıl ötesi aktif moddan geldiği bulundu.
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    First-principles calculations on mechanical and electronical properties of AlB2-type CaB2
    (Elsevier, 2024) Ahmed, Nabeel Ibrahim Ahmed; Parlak, Cihan
    In the present study, we focused on studying the properties of CaB2 in the hexagonal AlB2-phase. To determine the characteristics of the material, it is crucial to use first -principles calculation methods. Therefore, we used the Density Functional Perturbation Theory to calculate the elastic constants, phonon frequencies, and electron-phonon coupling properties of CaB2, which are important for understanding its superconducting and mechanical behaviors. Additionally, we analyzed Fermi surfaces and electronic band structures and compared them to those of MgB2. Our calculations showed that there is a close relationship between electron-phonon coupling and the superconducting properties of the material. We discovered that the critical superconducting transition temperature value is 24.71 K. In a remarkable finding, the presence of a Dirac cone at the Fermi level was observed in the electronic band structure, which may indicate that the material may be a topological semi -metal.
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    First-principles electronic structure and lattice dynamics of the giant dielectric compound Na0.5Bi0.5Cu3Ti4O12
    (IOP Publishing Ltd, 2008) Parlak, Cihan; Eryiğit, Resul
    We report the results of an ab initio study of electronic, dielectric, and lattice dynamical properties of high dielectric constant perovskite-derived oxide Na1/2Bi1/2Cu3Ti4O12. The calculations have been carried out within the local spin density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. The ground state is found to be an antiferromagnetic direct band gap semiconductor. Lattice dynamical properties, such as Born effective charge tensors, dielectric permittivity tensors, and phonon frequencies at the Brillouin zone center were calculated using density functional perturbation theory and found to be similar to the more studied CaCu3Ti4O12 and CdCu3Ti4O12 compounds. The calculated electronic (epsilon(infinity) approximate to 11.5) and static (epsilon(0) approximate to 150) dielectric constants indicate that the observed high dielectric constant is extrinsic in origin. The main contribution to the static dielectric constant is found to be due to a low frequency (50 cm(-1)) infrared-active mode which has a large mode effective charge.
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    First-principles study of the electronic structure and elastic properties of SrGa2 under pressure
    (Elseiver, 2021) Parlak, Cihan
    Determination of detailed electronic and lattice dynamical properties of hexagonal SrGa2 binary system under external pressure with the aid of first-principles calculation methods is of great importance in terms of the basic characteristics of binary system. On this basis, the phonon dispersion curves are calculated by the high-symmetry directions and related phonon frequencies parameters at the Brillouin zone center using density functional perturbation theory when the elastic constants are computed through the metric-tensor formulation. Besides, the fundamental quantities such as the electronic band structures, Fermi surface topologies, and detailed phonon dispersions are sensitively examined. At the same time, it is examined whether there is a close relationship between the determined properties and superconducting properties of SrGa2 material. However, the calculations clearly show that the information obtained directly from the electronic band structure and Fermi surfaces is insufficient to explain the superconductivity phenomenon of such materials.
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    Intercalation of graphite and hexagonal boron nitride by lithium
    (Springer, 2011) Altıntaş, Bahadır; Parlak, Cihan; Bozkurt, C.; Eryiğit, Resul
    Although graphite and hexagonal form of BN (h-BN) are isoelectronic and have very similar lattice structures, it has been very difficult to intercalate h-BN while there are hundreds of intercalation compounds of graphite. We have done a comparative first principles investigation of lithium intercalation of graphite and hexagonal boron nitride to provide clues for the difficulty of h-BN intercalation. In particular lattice structure, cohesive energy, formation enthalpy, charge transfer and electronic structure of both intercalation compounds are calculated in the density functional theory framework with local density approximation to the exchange-correlation energy. The calculated formation enthalpy of the considered forms of Li intercalated h-BN is found to be positive which rules out h-BN intercalation without externally supplied energy. Also, the Li(BN)(3) form of Li-intercalated h-BN is found to have a large electronic density of states at the Fermi level and an interlayer state that crosses Fermi level at the zone center; these properties make it an interesting material to investigate the role of interlayer states in the superconductivity of alkali intercalated layered structures. The most pronounced change in the charge distribution of the intercalated compounds is found to be charge transfer from the planar sigma states to the pi states.
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    ?-? phase transition of elemental cerium metal
    (IOP Publishing Ltd, 2022) Eryiğit, Serpil; Parlak, Cihan; Eryiğit, Resul
    The isostructural gamma-alpha phase transition in elemental cerium has been the subject of many experimental and theoretical studies over almost the past century without a universally agreed upon mechanism. here, we report the results of an extensive study of electronic and magnetic structures, f-electron number, entanglement entropy, and elastic properties of cerium in the GGA + U framework. We have found that almost all changes in the studied quantities mimic their behavior in the phase transition and could be related to the symmetry of the 4f occupation and the small change in Hubbard U near a critical value.