H.B. Ozisik

Structural, electronic, and elastic properties of K-As compounds: a first principles study.

First-principle calculations are performed to investigate the structural, elastic and electronic properties of K-As compounds (KAs in NaP, LiAs and AuCu-type structures, KAs2 in MgCu2-type structure, K3As in Na3As, Cu3P and Li3Bi-type structures, and K5As4 in A5B4-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to the Murnaghan’s equation of state) of the considered structures are calculated and reasonable agreement is obtained, and the phase transition pressure is also predicted. The repeated calculations on the electronic band structures and the related partial density of states are also given. The calculated second-order elastic constants based on the stress-strain method and the other related quantities such as Young’s modulus, shear modulus, Poissons ratio, sound velocities, Debye temperature, and shear anisotropy factors for considered structures are presented, and trends are discussed.

STRUCTURAL, MECHANICAL AND LATTICE DYNAMICAL STABILITY OF AgC AND AuC COMPOUNDS: A FIRST PRINCIPLES STUDY

Based on density functional theory, we have studied the structural stability, elastic, mechanical and lattice dynamical properties of AgC and AuC compounds for various structures: NaCl (B1), CsCl (B2), ZnS (B3), wurtzite (B4), WC (Bh), NiAs (B81) and CdTe. Generalized gradient approximation has been used for modeling exchange-correlation effects. The second-order elastic constants and related polycrystalline properties (bulk modulus, shear modulus, Youngs modulus, Poissons ratio, Debye temperature and sound velocities) have been calculated and discussed. We have also calculated phonon dispersion and phonon density of states of these compounds in all considered structures. According to the results, we found that, AgC compound is mechanically and dynamically stable in B81, B1 and B4 structures. Our results indicate that B81 and B3 are the candidate stable structures energetically, mechanically and dynamically for AgC and AuC compounds, respectively.

The stabilities, electronic structures and elastic properties of Rb As systems

The structural, electronic and elastic properties of Rb—As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3As in Na3As, Cu3P and Li3Bi structures, and Rb5As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghans equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Youngs modulus, the shear modulus, Poissons ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.

THE FIRST-PRINCIPLES STABILITY STUDY OF PdC AND CdC COMPOUNDS

We have studied structural, mechanical and dynamical properties of PdC and CdC compounds to predict the most stable structure. We have focused on seven binary structure types as rock salt (RS), caesium chloride (CsCl), zinc blende (ZB), wurtzite (WZ), tungsten carbide (WC), cadmium telluride (CdTe) and nickel arsenide (NiAs). For modelling exchange-correlation effects we have used generalized gradient (GGA) approximation based on Perdew–Burke–Ernzhorf functional (PBE). The polycrystalline elastic moduli such as Youngs and shear moduli, Poissons ratio, sound velocities, Debye temperatures and shear anisotropic factors have been presented for mechanically stable structures using second-order elastic constants calculated from the stress-strain relations. The results show that PdC is thermodynamically, mechanically and dynamically stable in ZB structure. On the other hand, while CdC is energetically in favor of RS structure, it is mechanically and dynamically stable in ZB structure.

THERMAL PROPERTIES OF THE XB2(X = Ag, Au) COMPOUNDS: A FIRST-PRINCIPLES STUDY

The thermodynamic properties of AgB2 and AuB2 compounds in AlB2 and OsB2-type structures are investigated from first-principles calculations based on density functional theory (DFT) using projector augmented waves (PAW) potentials within the generalized gradient approximation (GGA) for modeling exchange-correlation effects, respectively. Specifically, using the quasi-harmonic Debye model, the effects of pressure and temperature, up to 100 GPa and 1400 K, on the bulk modulus, Debye temperature, thermal expansion, heat capacity and the Gruneisen parameter are calculated successfully and trends are discussed.