Browsing by Subject "First principle calculations"

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    Band Structure and Optical Properties of Kesterite Type Compounds: First principle calculations
    (Institute of Physics Publishing, 2017) Palaz S.; Unver H.; Ugur G.; Mamedov, Amirullah; Özbay, Ekmel
    In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. 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 for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated. © Published under licence by IOP Publishing Ltd.
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    Dynamic nonlinear optical processes in some oxygen-octahedra ferroelectrics: first principle calculations
    (Taylor & Francis Inc., 2015) Simsek S.; Koc, H.; Palaz S.; Oltulu, O.; Mamedov, A. M.; Özbay, Ekmel
    The nonlinear optical properties and electro-optic effects of some oxygen-octahedra ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency- dependent complex dielectric function and the second harmonic generation response coefficient over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electro-optic susceptibility is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. The results for are in agreement with the experiment below the band gap and those for are compared with the experimental data where available. © 2015 Taylor & Francis Group, LLC.
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    Electron spectroscopy and the electronic structure of KNbO3: First principle calculations
    (Taylor & Francis Online, 2014) Simsek S.; Koc, H.; Trepakov, V. A.; Mamedov, A. M.; Özbay, Ekmel
    The electronic structures of KNbO3were calculated within the density functional theory, and their evolution was analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phase. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared the results with the theoretical spectra calculated within Density Functional Theory. The dominant role of the NbO6 octahedra in the formation of the energy spectra of KNbO3compound was demonstrated. The anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition. © 2014 Copyright Taylor & Francis Group, LLC.
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    Electronic and magnetic properties of zinc blende half-metal superlattices
    (A I P Publishing LLC, 2004) Fong, C. Y.; Qian, M. C.; Pask, J. E.; Yang, L. H.; Dag, S.
    Zinc blende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. We explore layered materials, consisting of alternating layers of zinc blende half-metals, by first principles calculations, and find that superlattices of (CrAs)1(MnAs)1 and (CrAs)2(MnAs)2 are half-metallic with magnetic moments of 7.0mB and 14.0mB per unit cell, respectively. We discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. We explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form.
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    Linear and non-linear optical properties of AgBO3(B=Nb, Ta): First principle study
    (IEEE, 2013) Şimşek, Şevket; Mamedov, Amirullah M.; Özbay, Ekmel
    The linear and nonlinear optical properties of ferroelectrics AgBO 3 (B=Ta, Nb) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. Specially, we present calculations of the frequency-dependent complex dielectric function ε(ω), and the second harmonic generation response coefficient χ(2)(-2ω,ω,ω) over a large frequency range in rhombohedral phase for the first time. The electronic linear electrooptic susceptibility χ(2)(-ω,ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. © 2013 IEEE.
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    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.
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    Optical properties of the narrow-band ferroelectrics: first principle calculations
    (Taylor & Francis Inc., 2015) Koc, H.; Simsek S.; Mamedov, A. M.; Özbay, Ekmel
    Based on density functional theory, we have studied the electronic, and optical properties of narrow-band ferroelectric compounds - (Ge,Sn) Te. Generalized gradient approximation has been used for modeling exchange-correlation effects. The lattice parameters of the considered compounds have been calculated. The calculated electronic band structure shows that GeTe and SnTe compounds have a direct forbidden band gap of 0.742 and 0.359. The real and imaginary parts of dielectric functions and therefore, the optical functions such as energy-loss function, as well as the effective number of valance electrons and the effective optical dielectric constant are all calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. © 2015 Taylor & Francis Group, LLC.