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Öğe Physical characteristics of Pb2FeSbO6 double perovskite for thermoelectric applications(Elsevier B.V., 2025) Caid, Messaoud; Rached, Djamel; Deligöz, Engin; Rached, Youcef; Rached, Habib; Irfani, MuhammadThe structural, mechanical, electronic, magnetic, optical, and thermoelectric properties of Pb2FeSbO6 double perovskite are investigated using full-potential linear augmented plane-wave (FP-LAPW) method incorporating the generalized gradient approximation (GGA) and GGA plus onsite Coulomb parameter (GGA + U). Pb2FeSbO6 crystallizes in a ferromagnetic (FM) cubic structure (space group Fm-3m) with lattice constants of 8.072 Å, in good agreement with experimental data. The compound exhibits ductile behavior, as assessed by Poisson and Pugh's ratios. It shows an integer magnetic moment of 5.00μB per formula unit and demonstrates semiconductor behavior with bandgaps as follows: under GGA, the band-gap is 2.347eV (Γ-X) in spin-up and is 1.208eV (X-Γ) in spin-down; under GGA + U, the band-gap is 2.923eV (X-Γ) in spin-up and is 1.665eV (X-X) in spin-down. Optical properties reveal strong absorption in the ultraviolet range, and thermoelectric evaluation suggests a promising figure of merit (ZTmax ≈ 1.0 at 300 K). These findings underscore the potential of Pb2FeSbO6 for thermoelectric and optoelectronic applicationsÖğe Small gas adsorption on metal clusters on trimer form of graphyne: First-principles density functional theory study(Elsevier B.V., 2025) Küçük, Hilal; Akça, AykanGraphyne has been a popular two-dimensional surface since its synthesis. Many studies have been contributed to the material science literature with graphyne due to its carbon-based nature, lightweight properties, and excellent properties. This research represents a first-principles study of the adsorption of small gas molecules (CO, NH3, SO2, NO, and NO2) on transition metal clusters (TM = Cu and Co) doped on graphyne. The cluster is designed with three metal atoms on a trimer form of graphyne. These two surfaces are formed with high stability with the binding energy of −3.91eV and −2.47eV. The geometric, magnetic, and electronic behaviors of the adsorptions are considered. ICHOP values are tested to demonstrate a deep understanding of bond strength. Although one configuration of CO molecule from the oxygen site physically interacts with the 3Co/GY surface, other molecules and CO from the carbon site attract with chemical interactions on both surfaces. All adsorptions have significant electron exchanges except the configuration of CO from the oxygen site and NH3 on Co-doped graphyne. Unlike other molecules, only NH3 molecules are electron donors. It is encouraging that 3Co/GY sensor might be able to detect NH3 at high temperatures.Öğe Understanding the pressure effect on the physical properties of half-Heusler semiconductor LiCaX (X = As, Sb, N) compounds from Ab-initio calculations(Elsevier, 2025) Çiftçi, Yasemin O.; Koçak, Belgin; Ateşer, EnginThe study delves into the structural, elastic, electronic, thermodynamic, and lattice dynamical and optic properties of LiCaX (X = As, Sb, N) ternary half-Heusler compounds under varying pressure and temperature conditions. Employing density functional theory with the generalized gradient approximation (GGA) in VASP codes, the initial steps involve optimizing the structure of the compound (cubic MgAgAs-type, space group F43m, C1b), determining elastic constants (C11, C12, and C44), and calculating elastic moduli (bulk modulus, shear modulus, Young's modulus). Other mechanical parameters such as Pugh's ratio, Poisson's ratio, and Zener anisotropy factor are also derived, providing insights into the brittle/ductile characteristics and isotropic/anisotropic behavior. The study further explores different vibrational modes in the compounds, and the effects of pressure on elastic anisotropy, vibrational, and optical properties are thoroughly investigated. Utilizing the quasi-harmonic Debye model, the research successfully reports V/Vo, bulk modulus, thermal expansion coefficient, and heat capacity at constant volume over a temperature range from 0 to 1000 K. The variation of photon energy is analyzed concerning the real and imaginary parts of the dielectric constant, refractive indices, extinction coefficient, reflectivity, and energy loss function up to 20 eV. The findings encapsulate the fundamental physical properties of all considered compounds, concluding with suggestions for potential future research avenues.Öğe Small gas adsorption on metal clusters on trimer form of graphyne: First-principles density functional theory study(Elsevier, 2025) Küçük, Hilal; Akça, AykanGraphyne has been a popular two-dimensional surface since its synthesis. Many studies have been contributed to the material science literature with graphyne due to its carbon-based nature, lightweight properties, and excellent properties. This research represents a first-principles study of the adsorption of small gas molecules (CO, NH3, SO2, NO, and NO2) on transition metal clusters (TM = Cu and Co) doped on graphyne. The cluster is designed with three metal atoms on a trimer form of graphyne. These two surfaces are formed with high stability with the binding energy of -3.91eV and -2.47eV. The geometric, magnetic, and electronic behaviors of the adsorptions are considered. ICHOP values are tested to demonstrate a deep understanding of bond strength. Although one configuration of CO molecule from the oxygen site physically interacts with the 3Co/GY surface, other molecules and CO from the carbon site attract with chemical interactions on both surfaces. All adsorptions have significant electron exchanges except the configuration of CO from the oxygen site and NH3 on Co-doped graphyne. Unlike other molecules, only NH3 molecules are electron donors. It is encouraging that 3Co/GY sensor might be able to detect NH3 at high temperatures.Öğe DFT assessment on the future prospects of inorganic lead-free halide double perovskites Cs2ABI6 (AB: GeZn, SnBe) for energy conversion technologies(Elsevier B.V., 2024) Caid, Messaoud; Rached, Habib; Rached, Djamel; Özışık, Hacı; Delig?z, Engin; Rached, YoucefIn this study, we employed density functional theory (DFT) calculations to investigate the structural, elastic, electronic, optical, and thermoelectric properties of Cs2ABI6 (AB: GeZn, SnBe) halide double perovskites (HDPs). We employed the full-potential linear augmented plane-wave (FP-LAPW) method, incorporating the generalized gradient approximation (GGA) and Tran-Blaha modified Becke-Johnson (TB-mBJ) approach for the exchange-correlation potential. We found that the HDPs are stable in a cubic structure (space group Fm-3m), as indicated by phase stability analysis, formation energies, tolerance factor, and elastic constants. The compounds exhibits ductile behavior, as assessed by Poisson's and Pugh's ratios. The electronic band structures of Cs2GeZnI6 and Cs2SnBeI6 exhibit indirect band gaps (X-L) of 1.124 eV and 1.551 eV, respectively, as calculated using the TB-mBJ approximation. Optical spectra were evaluated over the 0–13 eV energy range, including the dielectric functions, extinction coefficient, electron energy loss, refractive index, optical conductivity, reflectivity, and absorption coefficient. Additionally, we calculated thermoelectric parameters across a range of chemical potentials and temperatures to assess their suitability for thermoelectric applications. Our results suggest that these compounds are highly promising candidates for both optoelectronic and thermoelectric devices.Öğe Ab Initio Computational Materials Science(ICMATSE, 2024) Deligöz, EnginAb initio ((Latin for “from the beginning”) computational materials science is play an important role in accelerating the development and optimization of new materials. It is widely used in materials science. The aim is to simulate the properties of materials in order to understand and complement experiments. Scientists use these methods in the discovery of new materials, materials design, catalysis and chemical reaction mechanisms. Ab initio method (often referred to as firstprinciples methods) contains no experimental input other than the fundamental physical constants, making it possible to analyze the properties of systems that are difficult to characterize experimentally, or to predict the physical properties of materials that have not yet been made. We present an overview of the capabilities of ab initio methods in the structural and mechanical properties, illustrated with an example for 2D orthorhombic ?-GeSe compound using the VASP computer program.Öğe Impact of van der Waals corrected functionals on monolayer GeSe polymorphs: An in-depth exploration(Elsevier B.V., 2024) Kutluca, Abdullah; Deligöz, Engin; Özışık, HacıA comprehensive ab initio calculations were conducted to analyze the structural, electronic, elastic, and phonon characteristics of monolayer GeSe polymorphs, utilizing various van der Waals corrections. The physical properties of layered GeSe polymorphs were investigated using the Perdew-Burke-Ernzerhof exchange–correlation functional, implemented within a generalized gradient approximation. The study presents findings on the effects of the DFT-D3 and DFT-D3(BJ) functionals with Grimme correction on the ground state properties, with a focus on weak van der Waals interactions. The mechanical and dynamic stability of monolayer GeSe polymorphs is indicated by the analysis of the elastic constants and phonon dispersion curves. Monolayer GeSe polymorphs are found to have an indirect band gap semiconductor structure using HSE06 for the considered phases. The band gaps of these polymorphs are predicted to range from approximately 0.95 to 2.47 eV, which falls within a highly useful energy range for practical applications. Additionally, this study is the first to investigate the anisotropic mechanical properties of these materials.Öğe A first principles study of cubic IrO2 polymorph(Springer Nature, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Öztekin Çiftçi, YaseminWe have studied structural, thermodynamic, elastic, and electronic properties of cubic IrO 2 polymorph via ab initio calculations within the LDA and GGA approximations. Basic physical properties, such as lattice constant, bulk modulus, second-order elastic constants (C ij), and the electronic band structures are calculated, and compared with available experimental values. We have, also, predicted the Young's modulus, Poison's ratio (?), Anisotropy factor (A), sound velocities, and Debye temperature.Öğe Lattice dynamical calculations for the bcc cerium(Elsevier, 2005) Deligöz, Engin; Çiftçi, Yasemin; Çolakoğlu, KemalLattice dynamical calculations are performed on cerium with bcc structure using the improved third-neighbor Clark–Gazis–Wallis (CGW) model. The theory has been applied to compute the dispersion curves, frequency spectra, lattice specific heat, and Debye temperature of the bcc cerium. In general, the obtained results agree reasonably well with the experimental data at the high temperature of the bcc cerium which has been very recently measured by K. Nicolaus et al.Öğe Elastic, electronic, and lattice dynamical properties of CdS, CdSe, and CdTe(Elsevier, 2006) Deligöz, Engin; Çolakoğlu, Kemal; Çiftçi, Y.Ab initio calculations, based on norm-conserving pseudopotentials and density functional theory, have been performed to investigate elastic, electronic and lattice dynamical properties of chalcogenides (CdS, CdSe, and CdTe). The calculated lattice parameters, elastic constants, band structures, and phonon dispersions are in good agreement with available experimental and theoretical results. We also presented the pressure-dependence of elastic constants and the pressure-dependence of band gaps.Öğe First-principles studies on structural and electronic properties of ThN(AIP Publishing, 2007) Arslan, S.; Çiftçi, Y.Ö.; Çolakoğlu, Kemal; Deligöz, EnginWe present an ab?initio study of the structural and electronic properties of ThN. The plane?wave pseudopotential approach to the density?functional theory within the generalized?gradient approximation implemented in VASP(Viena Ab?initio Simulation Package) is used. The calculated lattice parameter, elastic constants and band structures are compared with the available experimental and the other theoretical results, and good agreement is obtained.Öğe The first?principles calculations on the CuI compounds(AIP Publishing, 2007) Yüce, G.; Çolakoğlu, Kemal; Deligöz, Engin; Çiftçi, Y.Ö.The ab initio total energy calculations, based on norm?conserving pseudopotentials and density functional theory, have been performed to investigate some structual, elastic, electronic and lattice dynamical properties of CuI in zinc blende (B3) and rock?salt (B1) structures. The calculated structural parameters, elastic moduli, band structures and the phonon dispersion curves are compared with the available experimental and the other theoretical works, and generally good results obtained. We have, also, presented the pressure dependent behaviours of the elastic constants for the same compound.Öğe Ab?Initio total energy calculations on the AlBi compound(AIP Publishing, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Çiftçi, Y.Ö.We present the results of the structural, thermodynamical, elastic, and electronic properties of the hypothetical aluminum bismuth (AlBi) compound (III?V) in zinc?blende phase by performing ab initio total energy calculations within the local density approximation in Siesta package. Particularly, we have focused on the pressure dependences of the second?order elastic constants (Cij), Debye temperature, and Melting temperature for this compound. Calculations on the other basic properties, such as lattice constant, bulk modulus, and some band structural parameters are also repeated and compared with those of other recent theoretical works, and generally, the good agreements are obtained.Öğe Structural, elastic and electronic properties of AlN: A first principles study(Wiley, 2007) Çiftçi, Y.Ö.; Çolakoğlu, Kemal; Deligöz, EnginThe brief results of the first-principles ground-state total energy calculations for aliminium nitrat (AlN) in zincblende and rocksalt structures are presented. Structural, elastic, and electronic calculations are performed using the SIESTA method with norm-conserving pseudopotentials. The obtained results are compared with the available experimental and other theoretical data, and the agreement is, generally, quite good.Öğe Electronic, elastic, thermodynamical, and dynamical properties of the rock-salt compounds LaAs and LaP(IOP Publishing, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Özışık, Hacı; Çiftçi, Y.Ö.We have studied the structural, elastic, electronic, thermodynamical and vibrational properties of LaAs and LaP in the rock-salt (B1) structure by performing ab initio calculations within the local-density approximation (LDA). Some basic physical properties, such as the lattice constant, bulk modulus, cohesive energy, second-order elastic constants (Cij), the electronic band structures, and phonon frequencies, are calculated and compared with the available experimental and other theoretical values. In order to gain further information, we have, also, predicted the Young's modulus, Poisson's ratio (?), anisotropy factor (A), sound velocities, and Debye temperature (?D), and reasonable values have been found. We also present the temperature-dependent behaviour of some thermodynamical properties such as entropy and heat capacity for these compounds in the B1 phase.Öğe Lattice dynamical calculations for the Ta–W alloys(Elsevier, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Çiftçi, YaseminLattice dynamical calculations are performed on Ta–W alloys with bcc structure in various concentrations. We assume ion–ion interaction through the improved third-neighbor Clark–Gazis–Wallis (CGW) model. The theory has been applied to compute the dispersion curves, frequency spectra and lattice specific heat of the studied alloys. The obtained results are in good agreement with the available experimental ones.Öğe The elastic, electronic, and vibrational properties of pure CdF2: A first-principles study(Elsevier, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Çiftçi, Y.O.Ab initio calculations, based on density functional theory and norm-conserving pseudopotentials, have been performed to investigate the some structural, elastic, electronic, and lattice-dynamical properties of pure CdF2. The calculated lattice parameter, phonon dispersion, and band structure are in accordance with the available experimental and other theoretical results. The pressure-dependent behaviours of elastic constants and band-structural properties of CdF2 are also reported.Öğe The first principles study on boron bismuth compound(Elsevier, 2007) Deligöz, Engin; Çolakoğlu, Kemal; Öztekin Çiftçi, Yasemin; Özışık, HacıWe have studied the structural, thermodynamics, elastic, and electronic properties of boron bismuth (BBi) compound in zinc-blende and rock-salt structures by performing ab initio calculations within the local density approximation. For the first time, we have calculated Debye temperature, melting temperature, phase transition pressure, phonon dispersion curves, density of state, and pressure dependences of the second-order elastic constants (Cij) for this hypothetical compound. Calculations on the other basic key properties, such as the lattice constant, bulk modulus, and some band structural parameters are also repeated and compared with the other recent theoretical works.Öğe The first principles study on the Boron antimony compound(Elsevier, 2007) Deligöz, Engin; Çolakoğlu, K.; Çiftçi, Y.O.We present the results of our calculations on Boron antimony (BSb) compound in zinc-blende (ZB) and rock-salt (RS) structures by performing ab initio calculations within the local density approximation (LDA). Some basic physical properties, such as lattice constant, bulk modulus, cohesive energy, phase transition pressure, second-order elastic constants (Cij), phonon frequencies, and some band structural parameters are calculated and compared with those obtained with other recent theoretical works. In order to further understand the behaviour of BSb compound, we have also predicted, the pressure-dependent behaviours of the band gap, second-order elastic constants (Cij), Young's modulus, poison ratios (?), Anizotropy factor (A), sound velocities, and Debye temperature for this hypothetical compound.Öğe The structural, elastic, and electronic properties of the pyrite-type phase for SnO2(Elsevier, 2008) Deligöz, Engin; Çolakoğlu, K.; Çiftçi, Y.O.We have studied some structural, thermodynamic, elastic, and electronic properties of pyrite-type SnO2 polymorph by performing ab initio calculations within the LDA approximation. The basic physical properties, in particular lattice constant, bulk modulus, second-order elastic constants (Cij), and the electronic structure, are calculated, and compared with the available experimental data. In order to gain some further information on the mechanical properties, we have also calculated the Young's modulus, Poison's ratio (?), anisotropy factor (A), sound velocities, and Debye temperature for the same compound.
