Optical properties of germanium dioxide in the rutile structure

Abstract.: We present first-principles calculations for the optical properties of germanium dioxide in the rutile structure. The electronic band structure has been calculated self-consistently within the local density approximation using the full-potential linearized augmented plane wave method. The electronic band structure shows that the fundamental energy gap is direct at the center of the Brillouin zone. The determinant role of a band structure computation with respect to the analysis of the optical properties is discusse

Optical properties of germanium dioxide in the rutile structure

We present first-principles calculations for the optical properties of germanium dioxide in the rutile structure. The electronic band structure has been calculated self-consistently within the local density approximation using the full-potential linearized augmented plane wave method. The electronic band structure shows that the fundamental energy gap is direct at the center of the Brillouin zone. The determinant role of a band structure computation with respect to the analysis of the optical properties is discussed

Structural, elastic, mechanical and thermodynamic properties of Terbium oxide: First-principles investigations

First-principles investigations of the Terbium oxide TbO are performed on structural, elastic, mechanical and thermodynamic properties. The investigations are accomplished by employing full potential augmented plane wave FP-LAPW method framed within density functional theory DFT as implemented in the WIEN2k package. The exchange-correlation energy functional, a part of the total energy functional, is treated through Perdew Burke Ernzerhof scheme of the Generalized Gradient Approximation PBEGGA. The calculations of the ground state structural parameters, like lattice constants a0, bulk moduli B and their pressure derivative B′ values, are done for the rock-salt RS, zinc-blende ZB, cesium chloride CsCl, wurtzite WZ and nickel arsenide NiAs polymorphs of the TbO compound. The elastic constants (C11, C12, C13, C33, and C44) and mechanical properties (Young's modulus Y, Shear modulus S, Poisson's ratio σ, Anisotropic ratio A and compressibility β), were also calculated to comprehend its potential for valuable applications. From our calculations, the RS phase of TbO compound was found strongest one mechanically amongst the studied cubic structures whereas from hexagonal phases, the NiAs type structure was found stronger than WZ phase of the TbO. To analyze the ductility of the different structures of the TbO, Pugh's rule (B/SH) and Cauchy pressure (C12–C44) approaches are used. It was found that ZB, CsCl and WZ type structures of the TbO were of ductile nature with the obvious dominance of the ionic bonding while RS and NiAs structures exhibited brittle nature with the covalent bonding dominance. Moreover, Debye temperature was calculated for both cubic and hexagonal structures of TbO in question by averaging the computed sound velocities

Holoprosencéphalie : A propos d’un cas

L'holoprosencéphalie (HPE) est une malformation cérébrale complexe résultant d'une division incomplète du prosencéphale, survenant entre le 18ème et le 28ème jour de vie embryonnaire et affectant à la fois le cerveau et la face. Trois degrés de sévérité croissante ont été décrits : l'holoprosencéphalie lobaire, semi-lobaire, et alobaire. Des anomalies de la face peuvent s'associer à la malformation cérébrale (leur gravité reflète grossièrement le degré de sévérité de l'holoprosencéphalie). Les étiologies sont essentiellement les anomalies chromosomiques et le diabète maternel. Le diagnostic repose sur l’échographie et l’IRM anténatales au troisième trimestre de la grossesse, la clinique, l’échographie trans-fontanellaire, la TDM et surtout l’IRM cérébrale. Le diagnostic génétique fait appel au caryotype. Nous décrivons un cas d’ holoprosencéphalie découverte après un accouchement survenu à 30 SA, chez une patiente primigeste de 26 ans, mal suivie, ayant une consanguinité du premier degré, non supplémentée en acide folique, et ayant pris du fenugrec au cours du premier trimestre de sa grossesse. Dans la majorité des cas, le pronostic est réservé.  

Optical properties of germanium dioxide in the rutile structure

We present first-principles calculations for the optical properties of germanium dioxide in the rutile structure. The electronic band structure has been calculated self-consistently within the local density approximation using the full-potential linearized augmented plane wave method. The electronic band structure shows that the fundamental energy gap is direct at the center of the Brillouin zone. The determinant role of a band structure computation with respect to the analysis of the optical properties is discussed

Full potential calculation of structural, electronic and optical properties of KMgF₃

A theoretical study of the structural, electronic and optical properties of KMgF₃ is presented using the full-potential linearized augmented plane wave method (FP-LAPW). In this approach, the local density approximation was used for the exchange-correlation potentials. First, we present the main features of the structural and electronic properties of this compound, where the electronic band structure shows that the fundamental energy gap is indirect. The contribution of the different bands was analysed from the total and partial density of states curves. The different interband transitions have been determined from the imaginary part of the dielectric function. The results are compared with previous calculations and with experimental measurements. The present work also deals with the behaviour of electronic properties, namely, the energy band gaps, and the valence bandwidth of KMgF₃ subject of hydrostatic pressures up to 30 GPa