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*Sürücü, Özge Bayraklı ( Aksaray, Yazar ) *Deligöz, Engin ( Aksaray, Yazar ), The anisotropic mechanical properties of Tl4Ag18Te11 compound was investigated elaborately for the first time by using Density Functional Theory calculations with the Vienna Ab-initio Simulation Package in this work. Tl4Ag18Te11 compound was optimized in the I4mm space group and the formation energy was determined as a negative value that is the indication of the experimental synthesizability of this compound. The optimized crystal structure was employed for the calculations of the elastic constants and the obtained values revealed the mechanical stability of Tl4Ag18Te11 compound. The polycrystalline properties were determined such as shear modulus, Poisson's ratio, etc. In addition, the anisotropic elastic properties were presented. The direction dependent sound waves velocities, polarization of the sound waves, enhancement factor and the power flow angle were determined. The thermal conductivity studies were performed and the minimum thermal conductivity (0.259 ​W ​m−1K−1) and the diffusion thermal conductivity (0.202 ​W ​m−1K−1) were calculated. This study illustrates the capability of this compound for the thermoelectric materials.

*Özışık, Hacı ( Aksaray, Yazar ) *Deligöz, Engin ( Aksaray, Yazar ), The electronic, optical, thermoelectric, and dynamic properties of Pb 7 Bi 4 Se 13 have been investigated using first principles calculations. The existence of heavy elements, bismuth and lead, has required to consider the spin–orbit coupling as implemented in the second variational procedure. It was observed that the upper of the valence band region appears predominantly from Se-p states with an admixture of Bi- p and Pb- p states, while the CBM comes mainly from Bi- p states only. The calculated optical properties illustrate a small manifold direct and indi- rect inter-band transitions emerging in the visible region. Semi classic Boltzmann theory was then employed to determine the Seebeck coefficient, electrical conductivity, thermal conductivity, and power factor. The phonon dispersion curve has been computed and explained. It can be deduced that the slight structural instability ob- served from phonon calculations is related to lower lattice thermal conductivity. Our findings were compared with the available experimental measurements, showing a good agreement.

WOS: 000340337200001, We used density functional theory (DFT) to study the structural, elastic, electronic, and lattice dynamical properties of tetragonal BiCoO3 applying the "norm-conserving" pseudopotentials within the local spin density approximation (LSDA). The calculated equilibrium lattice parameters and atomic displacements are in agreement with the available experimental and theoretical results. Moreover, the structural stability of tetragonal BiCoO3 were confirmed by the calculated elastic constants. In addition, the elastic properties of polycrystalline aggregates including bulk, shear and Young's moduli, and Poisson's ratio are also determined. The electronic band structure, total and partial density of states (DOS and PDOS) with ferromagnetic spin configuration are obtained. The results show that tetragonal BiCoO3 has an indirect band gap with both up- and down-spin configurations and its bonding behavior is of covalent nature. We compute Born effective charge (BEC) which is found to be quite anisotropic of Bi, Co and O atoms. The infrared and Raman active phonon mode frequencies at the Gamma point are found. The phonon dispersion curves exhibit imaginary frequencies which lead from the high-symmetry tetragonal phase to low-symmetry rhombohedral phase in BiCoO3. The six independent elastic constants, including bulk, shear and Young's moduli, and Poisson's ratio, complete BEC tensor and phonon dispersion relations in tetragonal BiCoO3 are predicted for the first time. Results of the calculations are compared with the existing experimental and theoretical data. (C) 2014 Elsevier Masson SAS. All rights reserved., Cukurova University [FEF2011D13, FEF2010BAP8], This work supported by Cukurova University under project number FEF2011D13 and FEF2010BAP8.

WOS: 000311503000024, By means of plane-wave density functional first-principles calculations within the generalized gradient approximation (GGA), we report the structural, elastic and mechanical properties of MB12 (M = Zr, Hf, Y, Lu) with UB12-type structure. The lattice constants, bulk modulus, elastic constants and related quantities such as Young's modulus, shear modulus, Zener anisotropy factor, Poisson's ratio and Cauchy pressure are calculated and compared with the available experimental and other theoretical data. A deeper understanding, the pressure variations of the lattice constants, bulk modulus, elastic constants and other mechanical properties are also analyzed in a wide pressure range (0-50 GPa) and their trends are discussed. Additionally, Mulliken population analysis is used to clarify the bonding nature of all compounds. Combining the bonding nature and the structural information, microhardnesses of all compounds are calculated theoretically and then the detailed comparisons between hardness and other mechanical properties such as bulk modulus and shear modulus are made. (C) 2012 Elsevier B.V. All rights reserved., Turkish Prime Ministry State Planning Agency [2011K120290], This work was supported by the Turkish Prime Ministry State Planning Agency under Projects No. 2011K120290.

WOS: 000301032100016, Based on density functional theory, we have studied the structural stability, elastic, mechanical, and lattice dynamical properties of BeB2, NaB2, and CaB2 compounds in AlB2, OsB2, and ReB2 structures, respectively. Generalized gradient approximation has been used for modeling exchange-correlation effects. Our calculations indicate that ReB2, AlB2, and OsB2 structures are energetically the most stable for BeB2, NaB2, and CaB2 compounds, respectively. The results show that these structures are both mechanically and dynamically stable. The bulk modulus, elastic constants, shear modulus, Young's modulus, Poisson's ratio, Debye temperature, sound velocities, and anisotropic factors are also calculated and discussed. Furthermore, the phonon dispersion curves and corresponding phonon density of states are presented. Our structural and some other results are in agreement with the available experimental and theoretical data. (C) 2011 Elsevier Ltd. All rights reserved.

WOS: 000301694500018, We have predicted structural, electronic, elastic, thermodynamic and vibration characteristics of TbN, using density functional theory within generalized-gradient (GGA) apraximation. For the total energy calculation we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab initio Simulation Package (VASP). We have used to examine structure parameter in eight different structures such as in NaCl (B1), CsCl (B2), ZB (B3), Tetragonal (L1(0)), WC (Bh), NiAs (B8), PbO (B10) and Wurtzite (B4). We have performed the thermodynamics properties for TbN by using quasi-harmonic Debye model. We have, also, predicted the temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities and Debye temperatures in a wide pressure (0-130 GPa) and temperature ranges (0-2000 K). Furthermore, the band structure, phonon dispersion curves and corresponding density of states are computed. Our results are compared to other theoretical and experimental works, and excellent agreement is obtained., Gazi University [05/2010-35], This work is supported by Gazi University Research - Project unit Project No: 05/2010-35.

WOS: 000300596000006, The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (B-h) and CuAu (L1(0)) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure. (C) 2011 Elsevier B.V. All rights reserved., Gazi University Research-Project Unit [05/2010-51], This work is supported by Gazi University Research-Project Unit under Project no: 05/2010-51.

WOS: 000296214300010, In this work, density functional theory calculations on the structural, mechanical, and lattice dynamical properties of AgB2 and AuB2 compounds in AlB2, OsB2, and ReB2 structures are reported. Generalized gradient approximation has been used for modeling exchange-correlation effects. The detailed information is given for the energetically most stable structure for AgB2 and AuB2 compounds. Specifically, the lattice parameters, bulk modulus, cohesive energies, elastic constants, shear modulus, Young's modulus, Poison's ratio, Debye temperature, sound velocities, and anisotropic factors are studied. The elastic properties are also studied under pressure. The phonon dispersion curves and corresponding phonon density of states are calculated and discussed. Our structural and some other results are in agreement with the available experimental and theoretical data. (C) 2011 Elsevier B.V. All rights reserved.

WOS: 000290650200002, The plane-wave pseudopotential approach to the density-functional theory within the GGA approximation implemented in Vienna Ab-initio Simulation Package (VASP) code have been used to calculate structural, elastic and lattice dynamical properties of praseodymium chalcogenides: PrS, PrSe and PrTe. The structural properties are performed in five different crystal structures: NaCl (space group Fm3m(225)), CsCl (space group Pm3m(221)), ZB (space group F43m(216)), WC (space group P6m2(187)) and CuAu (P4/mmm(123)). Our results showed that these chalcogenides are stable in NaCl phase which are in agreement with the experimental works. The phonon dispersion curves are showed that the gap between the optic and acoustic branches decreases on going from PrS to PrTe. We have also estimated some thermodynamical properties such as entropy and heat capacity at the temperature range 0-1000 K. (C) 2011 Elsevier B.V. All rights reserved.

WOS: 000282453500010, First principles calculations are performed to investigate the structural, electronic, elastic, and thermodynamic properties of the less known PrN compound for various space groups: NaCl(Fm3m(2 2 5)), C5Cl(Pm3m (2 2 1)), ZB(F43m(2 1 6)), Wc(P6m2(1 8 7)), and CuAu (P4/mmm (1 2 3)). Our calculation indicates that the NaCl type structure is energetically more stable than the other phases. The calculated lattice parameters are consisted with available theoretical and experimental results. Our band structure calculations show that PrN possessess a semi-metallic character for both with and without spin polarized (SP) cases. The calculated elastic constants satisfy the mechanical stability conditions at all considered pressures and the present values are significantly higher than those of the previous results. The related mechanical properties such as Zener anisotropy factor (A), Poisson's ratio (v), Young's modulus (E), and shear modulus (C) are also computed for NaCl structure. The temperature/pressure-dependent behaviours of bulk modulus, Debye temperature, heat capacity, thermal expansion coeffient, and V/V-0 ratio estimated within the quasi-harmonic Debye model., Gazi University [05/2009-16], This work was supported by the Gazi University Research-Project Unit under Project no. 05/2009-16.

We have investigated the structural, electronic, and optical properties of Zn1−xCaxSe ternary alloys using first principles calculations within the plane-wave pseudopotential method. Some basic physical properties, such as lattice constant, bulk modulus, electronic band structures, and optical properties (dielectric functions, refractive index, and energy loss function) were calculated. In addition, the effects of composition x on bulk modulus, band gap, refractive index and dielectric function were calculated. Our results agree well with the available data in the literature.

WOS: 000274222000019, A detailed theoretical study of structural, electronic, elastic, phonon, and thermodynamical properties of SmX (X = P, Sb, Bi) compounds is presented by performing ab-initio calculations based on density-functional theory using the Vienna ab-initio simulation package (VASP). For describing the interaction between electrons and ions, the projector-augmented wave (PAW) method is used. The generalized-gradient approximation (GGA) is chosen for the exchange-correlation functional. The calculated structural parameters, such as the lattice constant with and without spin-polarization (SP), bulk modulus, cohesive energy, second-order elastic constants, the electronic band structures and the related total density of states with and without SP and spin-orbit coupling (SOC) are presented. The high-pressure phase of all compounds is investigated and phase transition pressure from NaCl (B1) to high-pressure phase is determined. For B1 structure, the calculated values of lattice constants are compared with the available experimental and other theoretical data and bulk modulus values are compared with available other theoretical results. In order to gain further information, we have calculated Zener anisotropy factor (A), Poisson's ratio (nu), Young's modulus (E), shear modulus (C), elastic wave velocities, Debye temperature, phonon frequencies and one-phonon density of states for B1 structure of these three compounds. The temperature dependent behavior of heat capacity and entropy for these compounds in B1 phase is also presented. (C) 2009 Elsevier B.V. All rights reserved., Gazi University [05/2008-16], This work is supported by Gazi University Research-Project Unit under Project No: 05/2008-16.

We have investigated the structural and lattice dynamical properties of XB2(X=Sc,V,Ti) by using first-principles total energy calculations. Specifically, the lattice parameters (a, c) of the stable phase, the bond lengths of X–B and B–B atoms, phonon dispersion curves and the corresponding density of states, and some thermodynamical quantities such as internal energy, entropy, heat capacity, and their temperature-dependent behaviours, are presented. The obtained results for structural parameters are in good agreement with the available experimental and other theoretical studies.

We 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 (C-ij) 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. (C) 2006 Elsevier B.V. All rights reserved.

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 (C-ij), 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 (C-ij), Young's modulus, poison ratios (v), Anizotropy factor (A), sound velocities, and Debye temperature for this hypothetical compound. (C) 2007 Elsevier Ltd. All rights reserved.

Lattice 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. (c) 2005 Elsevier B.V All rights reserved.