Harun Akkus

Ab-initio calculation of band structure and linear optical properties of SbSI in para- and ferroelectric phases

An ab-initio pseudopotential calculation has been performed by using density functional methods within the local density approximation (LDA) to investigate the band structure and optical properties of the ferroelectric-semiconductor SbSI in the para- and ferroelectric phases. It has been shown that SbSI has an indirect gap in both phases (1.45 eV and 1.49 eV in the para- and ferroelectric phases respectively) and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV and 1.58 eV in the para- and ferroelectric phases respectively). Furthermore, it is shown that first-order phase transition, from the paraelectric phase to the ferroelectric phase (the transiton temperature is about 22 °C), does not change the nature of the band gap. Moreover, the linear frequency dependent dielectric function, including self-energy effects, has been calculated along the c-polar axis in the para- and ferroelectric phases.

Ab initio calculations of the electronic structure and linear optical properties, including self-energy effects, for paraelectric SbSI

The electronic energy band structure and linear optical properties of the ferroelectric semiconductor SbSI in the paraelectric phase are calculated by an ab initio pseudopotential method using density functional theory in the local density approximation. The calculated electronic band structure shows that SbSI has an indirect band gap of 1.45 eV and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV). The total density of states has been analysed. The linear energy dependent dielectric functions and some optical constants such as the absorption coefficient, extinction coefficient, refractive index, energy-loss function, reflectivity and optical conductivity, including self-energy effects, are calculated. The effective number of valence electrons and the effective optical dielectric constant are also calculated.

DENSITY FUNCTIONAL CALCULATION OF THE ELECTRONIC STRUCTURES OF SOME A5B6C7-TYPE CRYSTALS

The electronic band structures of some A5B6C7-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.

Band structure and optical properties of antimony-sulfobromide: density functional calculation

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.

Linear and Nonlinear Optical Properties of SbSI: First-Principle Calculation

Theoretical investigation of linear and non-linear optical constants of SbSI by using ab-initio method is made (in paraelectric and ferroelectric phase). Using an improved Kramers-Kronig technique with two confining spectral limits the spectra of optical parameters and linear and nonlinear optical functions were calculated.

Ab-initio study of the electronic structure and optical properties of KNO3 in the ferroelectric phase

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.

Structural and electronic properties of zincblende phase of TlxGa1−x AsyP1−y quaternary alloys: First-principles study

Using the first-principles band-structure method, we have calculated the structural and electronic properties of zincblende TlAs, TlP, GaAs and GaP compounds and their new semiconductor TlxGa1−xAsyP1−y quaternary alloys. Structural properties of these semiconductors are obtained with the Perdew and Wang local-density approximation. The lattice constants of TlxGa1−xAs, TlxGa1−xP ternary and TlxGa1−xAsyP1−y quaternary alloys were composed by Vegard’s law. Our investigation on the effect of the doping (Thallium and Arsenic) on lattice constants and band gap shows a non-linear dependence for TlxGa1−xAsyP1−y quaternary alloys. The band gap of TlxGa1−xAsyP1−y, Eg(x, y) concerned by the compositions x and y. To our awareness, there is no theoretical survey on TlxGa1−xAsyP1−y quaternary alloys and needs experimental verification.

First-principles investigation of structural, electronic, optical and dynamical properties in CsAu

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.

Ab-initio study of CsGeCl3 compound in paraelectric and ferroelectric phases

ABSTRACT 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.

Linear Optical Properties of Ferroelectric Semiconductor Bi2NbO5F Crystal

In this paper, we investigated the electronic band structure, total and partial density of states and optical properties of ferroelectric Bi2NbO5F structure with space group Pca21 using the density functional theory under the generalized gradient approximation. Our computational results show that Bi2NbO5F compound is a ferroelectric semiconductor with a narrow band gap. Due to anisotropy, linear optical properties of component were calculated for three crystallographic directions.