Pressure effects on the structural, elastic , electronic and optical properties of ZnO from first-principles calculations

First-principles calculations of the structural, electronic, optical and elastic properties of ZnO as a function of the pressure have been performed within density functional theory using Ultra soft pseudo potentials and generalized gradient approximation (GGA) for the exchange and correlation energy. Through our results, we note that the lattice constants decrease with the pressure increasing. Also, the elastic constants C11, C12, C13 and C33 and  the bulk modulus B increase with the pressure increasing. However, the elastic constants C44, the Shear modulus (G) and  Young’s modulus (E) decrease slowly with  increasing pressure, the band gap increases with the pressure increasing and ZnO has direct band. As pressure increases, the static dielectric constants ɛ1(0) and static refraction index n(0) decrease. Our calculated results are in good agreement with experimental data and other theoretical calculations.Keywords: DFT calculation, electronic, optical, elastic, under pressur

Electronic structure and magnetic properties of KXF3(X= Fe, Co, Mn, V) from ab initio calculations.

In this work we have performed first-principle calculations of the structural, electronic and magnetic properties of KFeF3, KCoF3, KMnF3, KVF3, using full-potential linearized augmented plane-wave (FP-LAPW) scheme within GGA. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Also, we have presented our results of the band structure and the density of states. The magnetic moments of KFeF3, KCoF3, KMnF3, KVF3 compounds are in most came from the exchange-splitting of X-3d orbital. Keywords: Magnetic materials; Ab initio calculations; Electronic structur

Structural and elastic properties of BiOCu0.875S with Cu vacancies : A First principles study

The  structural and elastic properties of BiOCu0.875S with Cu vacancies have been investigated by using the first-principles density functional theory within the generalized gradient approximation. Population  analysis  suggests  that  the  chemical  bonding  in  BiOCu0.875S  has  predominantly  ionic  character  with  mixed covalent−ionic character. Basic physical properties, such as lattice constant, elastic constants Cij, bulk modulus B, shear modulus G, were calculated.  The  elastic  modulus E and  Poisson  ratio ν  the ratio B/G, shear anisotropy  and elastic anisotropy βc/βa  were  also  predicted.  The  results  show  that  tetragonal  phase  BiOCu0.875S  is mechanically stable and behaves in a ductile manner.

Algebraic estimation in partial derivatives systems: parameters and differentiation problems

International audienceTwo goals are sought in this paper: namely, to provide a succinct overview on algebraic techniques for numerical differentiation and parameter estimation for linear systems and to present novel algebraic methods in the case of several variables. The state-of-art in the introduction is followed by a brief description of the methodology in the subsequent sections. Our new algebraic methods are illustrated by two examples in the multidimensional case. Some algebraic preliminaries are given in the appendix

AB-INITIO CALCULATIONS OF THE DIELECTRIC CONSTANT, OPTICAL ABSORPTION AND THE REFRACTIVE INDEX OF ZN1-XBEXO ALLOY

The optical properties of Zn1-xBexO were studied by first principle method using the density functional theory. The dielectric function and optical constants are calculated using PP-PW method within the generalized gradient approximation (GGA). The theoretical calculated optical properties yield a static dielectric constant for Zn1-xBexO are 4.08, 3.86, 3.60, 3.12 and 2.85 along polarization direction (001). It indicates that the static dielectric constants reduce with increasing Be concentration. However a static refractive indices for Zn1-xBexO are found to be 2.05, 1.98, 1.88, 1.77 and 1.70 with the increasing x, respectively. The obtained results agree well with the available theoretical and experimental values.