Browsing by Subject "Ab initio calculation"

Now showing 1 - 8 of 8

Open Access
Elastic and optical properties of sillenites: First principle calculations
(Taylor & Francis, 2020-04) Koç, H.; Palaz, S.; Şimşek, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions.
Open Access
Electronic band structure of rare-earth ferroelastics: theoretical investigations
(National Institute of Optoelectronics, 2018) Şimşek, Ş.; Uğur, G.; Uğur, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the electronic band structure and optical properties of RE2(MoO4)3 are investigated. The ground state energies and electronic structures were calculated using density functional theory (DFT) within the generalized-gradient approximation (GGA). The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant were also calculated. The main structure element in all our of compounds is the MoO4 tetrahedron. The presence of the MoO4 tetrahedra in the lattice of Gd2(MoO4)3, the similarity of the band structure and optical spectra of Gd2(MoO4)3 to those other tetraoxyanions of molybdenium demonstrate an important role of the MoO4 tetrahedra in the formation of the energy spectrum of Gd2(MoO4)3and other RE2(MoO4)3 compounds. This means that the MoO4 tetrahedra determine the lower edge of the conduction band and the upper edge of the valence band, and the conduction band is split into two subbands. The optical properties of RE2(MoO4)3 are in good agreement with this conclusion and previous experimental data.
Open Access
First principles prediction of the elastic, electronic, and optical properties of Sb 2S 3 and Sb 2Se 3 compounds
(2012) Koc H.; Mamedov, A.M.; Deligoz, E.; Ozisik H.
We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb 2S 3 and Sb 2Se 3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. 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. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. © 2012 Elsevier Masson SAS. All rights reserved.
Open Access
The mechanical, electronic and optical properties of Sn2P2S6 compound in different phases
(Taylor & Francis, 2021-12-01) Koc, H.; Palaz, S.; Simsek, S.; Mamedov, Amirullah M.; Ozbay, Ekmel
In present paper, the structural, mechanical, and electronic properties of the Sn2P2S6 compound under different pressures by the density functional methods in the generalized gradient approximation have been examined in the ferroelectric (Pc) and paraelectric (P2_1/c) phases. The lattice parameters, mechanical properties, electronic bands structures and partial density of states for both phases are presented and analyzed. The nonlinear optical properties and electro-optic effects of Sn2P2S6-Pc have been studied by the density functional theory in the local density approximation. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. We present calculations of the frequency-dependent complex dielectric function (ω) and the second harmonic generation response coefficient χ(2) (−2ω, ω, ω) over a large frequency range. The electronic linear electro-optic susceptibility χ(2) (−ω, ω, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for χ(2) (−ω, ω, 0) are in agreement with the experiment below the band gap and those for χ(2) (−ω, ω, 0) are compared with the experimental data where available.
Open Access
Optical and electronic properties of orthorhombic and trigonal AXO3 (A=Cd, Zn; X=Sn, Ge): first principle calculation
(Taylor and Francis Inc., 2016) Ozisik, H.; Simsek S.; Deligoz, E.; Mamedov, A. M.; Özbay, Ekmel
Electronic structure and optical properties of the CdXO3 and ZnXO3 (X˭Ge, Sn) compounds have been investigated based on density functional theory. According to the predictive results, reveal that the CdXO3 and ZnXO3 would be candidates for a high performance lead free optical crystal, which will avoid the environmental toxicity problem of the lead-based materials.
Open Access
The structural, elastic, electronic, and optical properties of Li₂RuO₃ compound in different structures
(Zhonghua Minguo Wuli Xuehui,Physical Society of the Republic of China, 2024-05-29) Koç, H.; Mamedov, Amirullah M.; Özbay, Ekmel
The structural, mechanical, and electronic properties of $Li_2RuO_3$ compound in $C2/c$, $C2/m$, and $P2_1/m$ structures are investigated using spin polarized generalized gradient approximation (GGA) for the exchange-correlation energy. It has been observed that the lattice parameter values ob tained as a result of the optimization are in good agreement with the experimental and theoretical values. The second-order elastic constants were calculated, and the other related quantities (bulk modulus, shear modulus, the Young’s modulus, Poisson’s ratio, anisotropy factor, sound veloc ities, and Debye temperature) have also been estimated. The electronic band structures of $Li_2RuO_3$ compound and the partial density of states corresponding to these band structures have been calculated. All three of these structures are semi-metallic. The spin-down states are metallic and the spin-up states are semiconducting. Finally, effective masses, the linear photon-energy dependent dielectric functions, and the energy-loss functions are also calculated and interpreted.
Open Access
Theoretical study of crossed and parallel carbon nanotube junctions and three-dimensional grid structures
(American Physical Society, 2004) Dag, S.; Senger, R. T.; Çıracı, Salim
This work presents a first-principles study of parallel and crossed junctions of single-wall carbon nanotubes (SWNT). The crossed junctions are modeled by two-dimensional grids of zigzag SWNTs. The atomic and electronic structure, stability, and energetics of the junctions are studied for different magnitudes of contact forces pressing the tubes towards each other and hence inducing radial deformations. Under relatively weak contact forces the tubes are linked with intertube bonds which allow a significant conductance through the junction. These interlinking bonds survive even after the contact forces are released and whole structure is fully relaxed. Upon increasing contact force and radial deformation the tube surfaces are flattened but the interlinking bonds are broken to lead to a relatively wider intertube spacing. The intertube conductance through such a junction diminish because of finite potential barrier intervening between the tubes. The linkage of crossing tubes to form stable junctions is enhanced by a vacancy created at the contact. The three-dimensional grid structure formed by SWNTs is also investigated as a possible framework in device integration.
Open Access
Topological semimetals in the ZrB5 (B ¼ Se, Te) materialclass: Weyl points and electronic properties
(Taylor & Francis Inc., 2024-02-20) Koç, Hüsnü; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the electronic structure, elastic parameters, density of states (partial and total), optical properties, and charge density of ZrB5 (B = Se, Te) have been investigated by means of first principles calculations. The generalized gradient approximation has been used for modeling the exchange-correlation effects. It has been observed that the calculated lattice parameter values are in agreement with the values in the literature. The second-order elastic constants were calculated, and the other related quantities have also been estimated. The electronic band structures and the partial density of states corresponding to these band structures of ZrSe5 and ZrTe5 are examined, and it is understood that ZrTe5 and ZrSe5 are narrow band semiconductors or semimetals. Finally, the electron energy loss function (ELS) spectra and charge density of ZrB5 are calculated and interpreted.