Y.O. Ciftci

Electronic, elastic, thermodynamical, and dynamical properties of the rock-salt compounds LaAs and LaP

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 Youngs modulus, Poissons ratio (ν), anisotropy factor (A), sound velocities, and Debye temperature (θD), 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.

First-Principles Calculations on Structure, Elastic and Thermodynamic Properties of Al2X（X=Sc,Y） under Pressure

To understand deeply the structural, elastic and thermodynamic characteristics of Al 2 X ( X = Sc, Y) compounds in C15 type (space number 227) Cu 2 Mg structure, we have performed ab-initio density functional theory within the local density approximation (LDA) and the generalized gradient approximation (GGA). The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. We have presented the results on the basic physical parameters, such as the lattice constant, bulk modulus, pressure derivative of bulk modulus, second-order elastic constants, Zener anisotropy factor, Poissons ratio, Youngs modulus, and isotropic shear modulus. In order to gain further information, the pressure- and temperature-dependent behaviour of the volume, bulk modulus, thermal expansion coefficient, heat capacity, entropy, Debye temperature and Gruneisen parameter were also evaluated over a pressure range of 0–20 GPa for Al 2 Sc and 0–17 GPa for Al 2 Y compound and a wide temperature range of 0–2000 K for both compounds. The obtained results were compared with the other reported values.

Lattice dynamical and thermodynamical properties of ReB2, RuB2, and OsB2 compounds in the ReB2 structure

Structural and lattice dynamical properties of ReB2, RuB2, and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation. The present results show that these compounds are dynamically stable for the considered structure. The temperature-dependent behaviors of thermodynamical properties such as internal energy, free energy, entropy, and heat capacity are also presented. The obtained results are in good agreement with the available experimental and theoretical data.

The structural, thermodynamical and elastic properties of TiO

In this paper, we have studied the structural, elastic, electronic and thermodynamical properties of TiO by performing ab initio calculations within the local density approximation (LDA). In particular, the lattice constant, bulk modulus, cohesive energy, phase transition pressure (Pt) from NaCl (B1) to CsCl (B2) structure, second-order elastic constants (Cij) and electronic band structures are calculated and compared with available experimental and other theoretical values. In order to gain further information, we have also predicted Youngs modulus, Poissons ratio (ν), anisotropy factor (A), sound velocities, Debye temperature (θD) and their pressure-dependent behaviours in the B1 phase.

First principles study of the structural, mechanical, phonon, optical, and thermodynamic properties of half-Heusler (HH) compound NbFeSb

We studied the structural, mechanical, phonon, optical and thermodynamic properties of MgAgAs-based NbFeSb compound by means of first-principles based on the density functional theory. The calculated lattice constant is in good agreement with the available experimental data. The electronic structure and corresponding density of states (DOS) were also calculated to give insight into the bonding mechanism and an indirect band gap was observed as ~1.77 eV, which is significantly higher than the previously reported one (0.529 eV). The elastic properties such as shear modulus, Youngs modulus etc under pressure, up to 65 GPa, were analyzed. The phonon dispersion curves, one-phonon DOS, and optical properties were obtained. In addition, the thermodynamic properties such as heat capacity, Debye temperature etc of NbFeSb were calculated at various temperatures and pressures by applying the quasi-harmonic Debye model.

A first-principles studies on TlX (X=P, As)

We present an ab initio study of the structural, electronic and thermodynamic properties of TlX(X=P,As). The plane-wave pseudopotential approach to the density-functional theory within the LDA and GGA approximations implemented in VASP (Viena Ab-initio Simulation Package) is used. The calculated lattice parameter, elastic constants, and band structures are compared with other available theoretical results, and good agreement is obtained. In addition, we have calculated the transition pressure (Pt) from zinc-blende (ZB) to (rock-salt) NaCl structures, and have examined some thermodynamic properties.

Electronic and optical properties of bilayer blue phosphorus

Abstract We investigate the electronic and optical properties of monolayer and stacking dependent bilayer blue phosphorus in the framework of density functional theory (DFT) and tight-binding approximations. We extract the hopping parameters of TB Hamiltonian for monolayer and bilayer blue phosphorus by using the DFT results. The variation of energy band gap with applied external electric field for two different stacks of bilayer blue phosphorus are also shown. We examine the linear response of the systems due to the external electromagnetic radiation in terms of the dielectric functions in the DFT theory. The relatively large electronic band gap and possibility of exfoliation form bulk structure due to weak interlayer coupling, make blue phosphorus an appropriate candidate for future electronic devices.

A large emitting area UV light source with semiconductor cathode

Light emission in the ultraviolet (UV) and visible (blue) range (330-440 nm) generated by a planar gas discharge system and the possibility of locally increasing the discharge light emission for a given photosensitivity of a planar GaAs semiconductor cathode has been studied. The use of metallic patched concentrators with an area of S=5/spl times/10/sup -4/ cm/sup 2/ and a density of 400 cm/sup -2/ leads to a fivefold increase in the gas light density. In a system with metallic patched concentrators, the local density of gas discharge light exceeds the density of uniform gas discharge light in the ionization system as many times as the working area of the semiconductor cathode exceeds the total area of the current concentrators. By using the infrared light to excite the semiconductor cathode of the system, we have shown that the uniform discharge light emission of the device with N/sub 2/ in the gap can serve as a source of UV radiation with a large emitting area of GaAs cathode if gas pressure and electric field are sufficiently high. Moreover, the use of metallic patched concentrators prolongs the working time of the cathode. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap, which changed the discharge from the Townsend to the glow type.

A first-principle study of the structural and lattice dynamical properties of CaX (X=S, Se, and Te)

We have studied structural, elastic, thermodynamic (Debye temperature and melting temperature), and lattice dynamical (phonon dispersion curves, heat capacity, and entropy) properties of CaX via ab initio calculations within the local density approximations. The results are compared with the available experimental and other theoretical data, and the agreement is, generally, quite good. We also predict the temperature and/or pressure-dependent behaviors of some mechanical, lattice dynamical, and thermodynamic properties for the same compounds.

The structural, thermodynamical, elastic, and vibrational properties of LaBi

In this study, we have studied the structural, elastic, electronic, thermodynamical, and vibrational properties of LaBi by performing ab initio calculations within the local-density approximation (LDA). In particular, the lattice constant, bulk modulus, cohesive energy, phase transition pressure (Pt) from the NaCl (B1) to the CsCl (B2) structure, second-order elastic constants (Cij), electronic band structures, and lattice dynamical properties were calculated and compared with the available experimental and other theoretical values. In order to obtain further information, we have also predicted Youngs modulus (E), Poissons ratio (ν), the anisotropy factor (A), sound velocities, Debye temperature (θD), and their pressure-dependent behaviour in the B1 phase. In addition, we have estimated the temperature-dependent behaviour of some thermodynamical properties, such as entropy and heat capacity from the lattice dynamical data.